Learn Node.js - Full Tutorial for Beginners

Hey, what's up guys, it's Pedro here from  New cutter calm. And in this tutorial,   we're gonna learn how to install Node j s, as well  as learn how to actually run code using node j s.   So to get started, we're going to actually have  to download node j s. So if you go to Google and   type node j s download, you should get a web page  similar to this. And I will be leaving a link in   the description in case you can't find it. So go  ahead and download eight, point three lt s. Now   once you download that, run it, install it enjoy  all that good stuff. And within these tutorials,   I'm going to be using Visual Studio code. And  if you don't know what Visual Studio code is,   it's an editor. Now, you can use whatever editor  you want. But the reason I'm using Visual Studio   code is because it has an integrated command  prompt. So once you download these two things,   I'm just going to head over to my desktop.  And let's create a new folder. And I'm just   going to say no JS tutorial. And now I'm just  going to head over to Visual Studio code. And   you should have a welcome screen like this, go to  File, Open Folder. And we are going to open the   folder that we just created. So I'm just going  to select this. And now I'm just going to hit   Ctrl N control and is going to create a new file,  I'm going to hit Ctrl S. And we are going to save   this file. And I'm just going to say app dot j s.  And this is going to be a very, very simplistic   JavaScript file. And we are just going to run it.  And this is just a test to see if you installed   node j s correctly. So if I hit console dot log  hello world, from node j s. Now if I save this,   and I'm actually going to exit out of this, but  you saw that this just popped up on my screen,   if I go to terminal, here is our command prompt.  So I'm just going to exit this to show you how you   can bring this up whenever you want to run code  using the terminal. So I'm just going to close   this. I'm going to hit Ctrl B, I am going to go  to View, I'm going to go to integrated terminal.   Now by default, Visual Studio code has it on  PowerShell. So if I go up here, you can notice   that mine says cmd. So if I hit Ctrl, Shift P and  type default, I can say select default shell. Now   I have three terminals installed on my computer,  you probably have PowerShell, and you probably   have command prompt. And I also have get, go ahead  and click command prompt. hit this plus button,   this is going to bring up a new terminal. So if  I was to hit this or bring up another CMD, and   this should say cmd. So I'm just going to remove  for me, I'm going to remove one, since I already   have one open. And now all I'm going to do is type  node, and then the name of the file. So the name   of the file that we just created was called app  dot j s. And here we go, we get an output of hello   world from node j s. Now let's say that you're  not using Visual Studio code for whatever reason   you have your own editor of choice, what you can  do is you hit the start menu, type cmd and then   go to command prompt. And then you can see that  we get something very similar to the integrated   command prompt, but we're in a different location.  So if I go to my desktop, open this folder. Let's   copy the path that this folder is located. So I'm  just going to hit Ctrl C to copy, head over to my   command prompt. I'm just going to type C the CDs  stands for change directory. All that means is hey   change folder. So right now I am in a folder  called users Pedram makhado. I need to be in   this folder. So now I'm just gonna click this. Go  down to edit, click paste. And that's our path. So   now if I hit Enter, you can see that our path has  changed. And now if I type node app.js You can see   that we get a Hello World from node. So either way  is fine. If you want to use Visual Studio code and   its integrated terminal, you're more than welcome  to, if you're using a different editor and it   doesn't have its own integrated terminal, you're  more than welcome to use the command prompt.   In this tutorial, we're going to be talking about  node modules, or a node module is is basically   a JavaScript file. It's a way to separate  concerns for our application. So for example,   let's say that I have an app.js file. And in  this app.js file, I have maff, a bunch of API   requests and database calls. Instead of putting  them all on one file, what we can do is separate   each of those concerns into their own files. So  to get started, I'm just going to hit Ctrl. B,   I'm going to say Ctrl N. So we're going to create  a new file. And I'm just going to say Ctrl S and   we're going to save it as the tutorial, dot j s.  Let's save that Ctrl B. And now we could focus on   this new file or this new module called tutorial  dot j s. So to get started, let's actually give   our tutorial module something. So I'm going to  give it a function. So I'm going to say const,   some, and it's going to have two parameters, and  all it's going to do is add and return them. So   number one plus number two. Next, what I want to  end up doing is I want to expose this function   to the outside world. Because right now, if I hit  Ctrl S, and if I was to try to use this function,   so I'm just going to delete this. So if I was  just to say sum, one plus one. And if we were   to actually run this, you can see that we get  an error, some is not defined. So you might be   saying, why is some not defined, I just defined it  here. Well, I need to expose this function for the   outside world to use. So I need to let know know  that this sum function within my tutorial module   is available to be used. So in order to do that,  or I need to do is type module exports, and pass   it in some like so. Now that this is available to  be used, I need to tell my app.js file where this   sum function is located. So what I can do here  is declare a variable. So I'm just going to say   Kant's. tutorial. And now I'm just going to use  the word require. And then we're going to give   it a path. Now the path is dot forward slash.  So where did I get dot forward slash from? dot   forward slash means that it's within the same  exact path that this file is currently in where   app dot j s. So if I was to hit Ctrl, B, you  can see that I that j s is on the same level   as the tutorial dot j s, and that they're in the  same folder called Node JS tutorial. So if I hit   Control V, again, get rid of that. And then I  pass in the name of the file, which is obviously   tutorial dot j s. Now you do not need to pass in  the extension, all you need to do is pass in the   name of the file, Node. js automatically assumes  that it is a JavaScript file. And now, if I was to   print out tutorial, two, let's see what's inside  it. And now let's get rid of our son call. We're   gonna call some a little bit later, I just want to  show you what the variable tutorial has. So if I   was to save this, and let's scroll down, I'm going  to type CLS, hit enter. That's going to clear   the terminal. And now I'm just going to run node  app. And you can see that the tutorial now holds   a function called sum from our tutorial module. So  now if I want to actually use that function, I can   say tutorial and pass in one plus one. And let's  actually print out the results. I'm just gonna say   console dot log it. Let's save it, execute it  again. And you can see that we get our desired   output of too and that we are indeed importing  from our tutorial module, the sum function. So now   that we know how to do that, how will we import  ml To pull stuff from modules. So for example, if   we head back to our tutorial module, let's say I  have multiple functions or multiple variables, or   even a class, how do I export more than one thing?  Well, what you can do is I can say, and just for   the sake of example, let's add more stuff. So I  could say Kant's. Hi, and just gonna set this the   3.14. And let's create a class. And I'm gonna say  some math object. Let's give it a constructor. And   I'm just gonna say object created. Okay, so now  I have some pi and some math object. Now, I want   all three of these to be exposed to the outside  world. So that app.js, for example, can require   them and then use it. So how do I do that? Well,  one way to do that is to add properties to the   module dot exports object. So for example, I could  say dot sum. And I'm just going to copy this. So   now experts, that sum is going to have the sum  function exports.pi is going to hold the value   of 3.14. So I just set it equal to pi. And some  math object, it's going to be madrona exports dot   some math object is going to be equal to some math  object. Now if I was to save this, head over to   app, and let's just remove this for now, I want to  print out what tutorial is holding once we require   from our tutorial module. So if I save this, and  now let's execute this, you can see that we're   getting an object back tutorial is now an object.  And now this object has the properties of sun. And   it tells you that it's a function, pi, the value  of pi, and some math object. And you can see that   it's our class. And now if I want to execute this,  it will be like accessing a normal object. So for   example, we have tutorial. And let's say we want  to use the sum function. So just saying tutorial,   and I'm passing the two numbers, I could say  tutorial, sum, and pass in the two numbers. And   I'm just going to copy this. Let's paste this  two more times. And now if I want to print pi,   package, say tutorial, pi. And within here, the  same thing for the object, I can say new tutorial,   dot some math object. And that's going to create  a new instance of our some math object. And now   if I was to save this, and run it, you can see  that it executes as expected. So tutorial sum,   gives us to pi has the value of 3.14. And you  can see that our constructor gets executed   object created. One more thing to show you before  I wrap this up, if this is an ugly syntax for you,   for example, saying module dot exports, that sum  equals this module.exports.pi is a bit repetitive,   what we can do is, instead of exporting each of  these individually, I'm going to let's remove two   of them. And instead, what we can do is export  an object literal and tag along the properties.   So I could say sum is going to be some pie.  This is going to be pi. And then some math   object is going to be some math object. And  if I'm to save this, and now execute it, we   should get the same exact result. So let's execute  that. You can see that it's working beautifully.   And this tutorial, we're going to be talking  about the events module, particularly the event   emitter class within the events module. Now all  the events module allows us to do is basically   bring Event Driven Programming to node j s. So  to get started, we're going to actually have to   require the events module. Now the events module  is actually built into node j s. So I'm just   going to say Kant's. Event emitter. Now this is  going to be the class that we get from requiring,   from the events module, I was just gonna  say equals require event. Now from here,   we're going to have to create a new instance of  the event emitter. So I'm just going to say const,   event emitter, I say, new event emitter.  So from here, we're going to start getting   into Event Driven Programming. Now that I have  my event emitter object, let's actually attach   a listener to it. So I'm just going to say event  emitter. And I'm going to call the method on now,   this method takes on two arguments. One is the  listener that you want to attach to this object.   So I'm just going to call it tutorial for this  example. And the second argument is going to be   the function that you want to execute. When does  the tutorial event occurs. So let's just pass in   this function. And I'm going to say is console dot  log tutorial event has occurred. So now if I save   this and run it, so I'm just gonna hit Ctrl S to  save. And I'm just gonna say node app, you can see   that nothing happens within our terminal. Now, why  is that? Well, I have this object. I've attached a   listener call tutorial. But I haven't emitted  a tutorial event. Remember, this code here,   is only going to be executed when a tutorial event  occurs. So now let's emit a tutorial event. So I'm   just going to say event emitter. And now I'm just  going to pass in tutorial as the first argument.   And that's it. So now, if I was to hit Ctrl,  S to save, and now execute this one more time,   you can see that our tutorial event gets triggered  whenever we call the emit method. So now what   happens when we actually want this function to  have parameters? Well, I could give a parameter   so I could say num, one, num, two. And just for  argument's sake, so just to show on the console,   we're going to print out the sum of number one and  number two. So now how would I call it down here   with the emit method? Well, I'll just pass it in  an argument. So I could pass in one, and two. So   if I save this now, and now go to node app, you  can see that we get the value of three. So you   just pass in the argument. Now, this is all fine  and dandy. But how would I create a custom object   which takes advantage of using events? Well, I  could just inherit from the event emitter class.   So for example, let's say that I want to create a  person class. So I say class person. And I could   just extend from the event emitter class. And  now from here, let's give it a constructor. Now   let's call our super function. So I'm just going  to say super. And this is going to allow us to   use that this property within our class. And now  I'm just going to say this, that underscore name   is going to be assigned value name. And now let's  actually pass in name to our constructor. And now   let's give this person class a getter. So I'm just  going to say get name. And all this is gonna do is   just return this dot underscore name. So now that  we have our person class defined, let's actually   create a new instance of it. So I'm just going to  go down here. And I'm just going to say, let Pedro   equals new person. And let's pass in Pedro. And  now here remember, when I say new person, person   extends the event emitter class, which means that  Pedro is also an instance of the event emitter   class. So now I can add a listener to the page  or object so I could just say pedro.on and And   I'm just going to call it name. And we're going  to pass in our function. And I'm just going to   print out my name is so and so. So I'm just gonna  say console. dot log, my name is. And we're just   going to say Pedro dot name. So now that we've  attached our listener, obviously, we're going   to have to call the emit method. So we're gonna  emit the event has occurred. So I'm just gonna say   Pedro dot emit, and we're gonna pass in name. And  now if I was to save this, and now execute this,   you can see that we get the desired output  of my name is Pedro. So that's how you would   extend using the event emitters class. And for our  final example, let's say that we have more than   one person object, so I'm just going to create a  new person, I'm just going to call let's make it   a girl, I'm just going to call her Christina. I'm  going to say new person. And we're going to pass   in Christina. Now let's add a listener to the  Christina object. So I'm just gonna say Christina,   that on name. And you could use a loop for this.  But since I'm only creating two person objects,   that doesn't make sense for this example, but you  can use a loop to do this on one shot. And we are   just going to copy this. paste this in here, I'm  just gonna say, Christina, that name. Alright,   so why did I go there to bother are showing  you that we create it to person objects,   and attach listeners to it? Well, what I want to  show you is that when you emit an event to occur,   the event gets executed synchronously. So for  example, if I say, Pedro, and I say, Christina,   and now if I was to save this, and now execute it,  you can see that these get executed synchronously.   So because Pedro emitted first, Pedro gets  executed first and then our Christina object,   so they get executed in the order that they  admitted in so they execute synchronously.   In this tutorial, we're going to be talking about  the read line module. Now, what the read line   module allows us to do is prompt the user as well  as get user input. So to get started, we're going   to have to require the module. So I'm just going  to say const. reline is equal to require read   line, and this is going to bring in our relying  module. Next, we're going to have to create an   instance of the read line interface by using the  Create interface method. So I'm just going to say   read line dot create interface. And within here is  going to take an object. Now we're going to give   this object two properties. And this is basically  our configuration file. So the first property I'm   going to give it is input. And then we're going  to give it an object. Now this object is called   process not process is a global object. So you  don't have to require it. It's already given to   us by node. And here we're going to say STD. And  now input is going to be the STD in input stream.   And then here, we obviously need an output. So  I'm just gonna say output, and we're going to   give it process that STD out. And that's going to  stand for output stream. Now, when this method is   executed, is going to return our read line or the  face object. So let's save it inside a variable   so we can use it. So I'm just gonna say const RL  is equal to this. Now let's say I want to ask the   user what two numbers added together are equal to.  So for this example, I'm just going to generate   two random numbers between one and 10. So I'm just  going to say let num one equal math floor math dot   random. And we're going to times this by 10. And  we're going to shift that over by one. So this is   going to give us a random number between one and  10. It's copied us twice. Paste that, too. And we   need the answer. So I'm just gonna say less Answer  equal number one plus number two. All right. So   now that we have this, we're ready to ask the  user what these two numbers are equal to. Now in   order to do that, I'm going to use our read line  interface. And our relying interface has a method   called question. So I'm going to say RL question.  Now, the first argument is going to be a string,   the second argument is going to be a function. And  basically, the first argument is going to be the   question we would like to ask the user. So I'm  just gonna say back tick, what is not one plus   num two? Question mark. And I'm just going to  hit enter here, because I want you guys to see   this on one line. And we're going to include our  callback. Now, this function is going to get the   user input as a parameter. So I'm just gonna say  user input. And for now, I'm just going to print   out user input onto the console, just so you guys  can see that it's actually working. So now if   I was to save this, head over to my console type  node app, it's going to say what is four plus two,   I'm going to say banana. And there you go, it  prints out the user input. It's important to   note that if you take a look at our console,  the application is still running. So I'm just   going to hit Ctrl. C to break out of it. And what  we need to do is actually close the read line   interface when we're done using it. So in order  to do that, let's actually add a couple of things.   First thing, I want a new line, right after this  question mark here. So I'm just gonna say forward   slash n. So when I prompt the user, the users  input instead of lining up right next to it,   like so there's gonna be underneath. Alright, so  I fixed that problem. Next thing I want to do is   actually test the user input to see if he actually  got the answer. Correct. So in order to do that,   I'm just going to say, if user input. And it's  always important to trim the users input, if you   ever accept anything from a user, just to get rid  of the trailing whitespace. And we're just going   to say if the user's input is equal to answer.  So if they answer the math question correctly,   I want to close the application. So I could say,  RL dot close. And here, and now if I was to save   this, and now execute the program, so I'm just  going to write node app. And it's going to say,   What is 10 plus four, and I'm going to answer with  14. And you can see that we answered it correctly,   and therefore our application closed. Now, what I  want to do is actually add a listener to the close   event. Now, the read line interface is actually  an instance of the event emitter class. So what we   can do is actually scroll down here. And I'll add  it towards the end. And I want to say our own.on.   And basically, I'm going to say, hey, I want you  to listen for an event to occur, I'm going to say   close. And we're going to give it a callback.  And this function is only going to execute when   we close the reline interface. So now I'm just  going to say console dot log. And basically,   I just want to let the user know that Hey, you got  the correct answer. So I'm just gonna say correct.   So now if I was to save this, and now execute  it, node app, what is six plus three, I'm just   gonna write nine. You can see that correct, gets  printed out onto the console. Now correct gets   printed out onto the console. Because when we  use the method close, it emits the close event.   And since we're listening for a close event, this  callback function gets executed. And on that note,   I better add a semicolon on there. And let's see  that. So now that we handled what happens when the   user inputs correctly, what happens if the user  gets the wrong answer? So in order to do that,   let's create an else statement within our  question method here. So I'm just going to   say else. And what I want to do basically is re  prompt the user. So I'm just going to say rl.com.   That set prop. And set prompt is basically going  to take an argument of string. And it's going to   ask the user, basically what you want to know. So  I'm going to say to the user, incorrect response,   please try again. And let's add a new line here.  And now in order to use the Prop, I actually have   to call it. So the first method is to set the  prop. The second method is going to be to call on   discussing our prompt. So now, I'm just gonna hit  Ctrl. S to save. And now I'm just going to execute   this node app. And he's gonna say what is one plus  five, and I'm going to say banana. And it's gonna   say incorrect response, please try again. Now,  I actually haven't told it what to do once the   user inputs. So let's actually write the code for  that. Now, what I'm going to do is actually add a   listener to our read line interface. So I'm going  to listen for the users input. And the event for   that is rl.on. Mine. And then we're going to pass  it in our callback. Now this callback is going to   have the user's input. And now we're going to  decide what to do once we get the user's input.   So obviously, what we want to do is check if the  user's input is correct. And if it is correct, we   are going to close the application. And now what  happens if it isn't correct, we're gonna say else.   And then I'm going to reset the prompt. So I'm  just gonna say R dot set prop. And I'm gonna say,   let's actually make this more informative. So I'm  just gonna say your answer. And then we're just   going to print out what they wrote. user input,  is and correct. And we're going to build a forward   slash. And before that, I'm just going to say, try  again. So now let's enter. And now remember, once   we set the Prop, we actually have to call it. So  now I'm just going to say RL dot prop. And now if   we just take a look at what we have so far, this  is basically going to give us a loop. So we set   a line event listener. Now when the user enters  input that's going to trigger this line input,   we're going to test to see if what he gave us is  correct. And if it is, we're just going to close   that but patient. And if we close the application  this on close method is going to execute,   it's going to say, correct. So now let's see what  happens if we give it the wrong value. Is it going   to execute the else statement? And it's going  to set the prompt your answer have so and so   is wrong. And that is going to prompt the user  again. And basically, this line event is going to   keep executing until the user enters the correct  input. So let's actually take a look at this in   action. So I'm just going to clear the terminal.  And before I execute, let me just say, intro as to   say, oops, Ctrl S to save. And now I'm just going  to hit node app. And it's gonna say what is one   plus four, I'm going to say banana. Incorrect  response, please try again, I'm going to type   banana again, your answer banana is not correct.  And you can see that this will go on indefinitely.   Now, if I go back up, and let's actually see  what it was, what is one plus four, I'm just   going to type in five. And you can see we get the  output of correct and then exit the application.   And this tutorial, we're going to be talking about  the file system module. Now what the file system   module allows us to do is work with the file  system. And what I mean by that is that it allows   us to create files, read files, delete files,  create folders, stuff like that. So to get started   We're going to have to require the file module  into our project. So I'm just gonna say const Fs   is equal to require Fs. So now that we have the  file system module within our node application,   let's actually use it. Now. If I hit Ctrl, B,  you can see that all I have is my app.js file   within my Node JS tutorial folder. So let's  actually create a file. So this one's gonna   create a file. And we're going to say Fs dot  write file. Now, the first argument is going   to be the name of the file. So I'm just going  to say example, dot txt. The second argument is   what you want to write to the file. So I'm just  going to say, this is an example. And the third   argument is going to be a callback, and this  callback is going to have a parameter of error,   in case anything goes wrong. So I'm just gonna  say error. There we go. So let's actually finish   writing this. So I could say, if error, we're  just going to print out the error. Otherwise,   we can say, file successfully created. So I'm  just gonna write file successfully created. So   now if I was to save this, and let's run this node  app, you can see that we get file successfully   created. And now if I hit Ctrl, V. good not to be  in the console. And when I do that, Ctrl B. Now,   you can see that we have a newly created file  called example, dot txt. And if we look in it,   we see the data that we wrote to the file. Now  that we created this file, let's actually read it,   let's open up and read it. So if I was to say Ctrl  V again, and I'm just going to go to App dot j, s,   and within this else statement, let's put all  this code within here. And now I'm going to say   Fs dot read file. And within here, the first  argument, much like the right file method, is   going to be the name of the file that you want to  read. So I'm just going to say example, dot txt,   the second argument is going to be the encoding  type. Now I'm going to leave this blank because   I want to show you guys what happens when you  don't leave an encoding type. And then the third   argument is going to take a callback function.  And this callback function has two parameters,   it has error, and it has the file that you  actually want to read. Now in here, I actually   want to show you guys what the file looks like.  So we're going to do the same thing that we did   and the right file method, I'm going to check if  there's any errors. And if there are no errors,   I just want to print the file itself. So now if  I was to save this, go to node app. Now you'll   see that the file was successfully created. And  then you see that when we print out the file,   we get this buffer stream. And then we get this  bunch of numbers following it. Now the buffer   stream stores data and binary. Okay. So what we  need to do is specify the encoding type that we   want it to be displayed as. So up here, we're  going to go up here. And I'm just going to pass   in you TF a. So that's the encoding that I want.  And now if I was to save this, go to node app. You   can see that file was successfully created. And  we're successfully reading the contents within the   file. Alright, so now that we know how to create  and read files, let's actually cover a few more   methods. So what I want to do is start with a  fresh examples. I'm just gonna comment this all   out. I'm just going to highlight everything Ctrl  backslash, and that's going to comment everything   out for me. Now what I want to do is let's say  that when I created this example dot txt file,   that I really didn't mean to call example dot  txt, let's say I wanted to call it example to,   for instance, well, I could use the Rename method.  So I could do something like this, I can say Fs   dot rename, and rename is going to take in three  arguments. The first argument is going to be   example, dot txt. And that's going to be the name  of the file that we want to rename. The second   argument is going to be what we want to rename the  file to. So I'm just going to say example two, dot   txt. And the third argument is going to be their  callback function, which has a parameter called   error. And we're going to do the same thing, as  we've been doing for all these asynchronous calls,   we're just going to say, if error, we're just  going to print that out to the console. If there's   no error, and everything went fine, we're gonna  say successfully rename the file. So I'm just   gonna say successfully rename the file. So now,  if I hit Ctrl, S to save, and now let's run this,   you'll see successfully renamed the file.  And it says the leader from this, and that's   probably because it hasn't updated yet. So if I  close this, and I'm just gonna hit Ctrl, B. And   you can see that within our package explorer,  that our file has been renamed to example two,   dot txt. And if I open this as the same exact  file that re created, couple more methods that   I want to go over. So I'm just going to hit Ctrl.  B. And let's say that, once I comment this out,   let's say that when I was creating the file that  I forgot to add something towards the end of the   file, so what do you want to do, I want to append  data to the file. So I'm just going to say Fs that   a pen file is going to take in three arguments,  it's going to take in the name of the file, I'm   just going to say example, two dot txt, the second  argument is going to be the data that you want   to append to the file. So I'm just going to say  some data being upended. And the third argument   is going to be the callback function. And this  is going to have an error as a parameter passes   and, and we're gonna say if error printed out to  the console. Otherwise, we're gonna print out that   we successfully appended data to the file. So I've  successfully appended data to file. I'm just gonna   move this over so you can see. And now if I save  this, and execute this, so node app, you'll see   successfully appended data to the file. So let's  actually take a look at our file. And you can see   that our file has been changed. So before we had  this as an example, and then we appended on data   to the end of the file. And the last method that  I want to cover within this tutorial is how do   I delete a file. So for example, we did all this  and let's say that I've had enough with this file,   I just want it gone. So let's just comment this  out. And this is going to be the final method that   I go over. So we're just gonna say Fs dot unlink.  And the first argument is, obviously, you guys   should get this by now. It's going to be example,  two. Example two dot txt. And the second argument   is going to be a callback function and have the  parameter of error. And within here, if ever   printed out to the console, if there's nowhere  where we're just going to say successfully deleted   the file successfully. So now if I was to save  this, and now execute it, you can see successfully   deleted the file status up here deleted from  this. So if I close this, and if I was to   hit Ctrl B to bring up the package explorer,  you can see that the file I no longer exist.   And this tutorial is going to be part two of  my file system modules tutorial. Now in the   previous tutorial, we went over using the file  system module to work with files. And this I   want to go over how to work with folders. So to  get started, we're going to have to require the   file system module. So I'm just going to say  const, Fs equals require, and then Fs here.   Alright, and now what I want to do is I'm going  to say fs.mk Dir. And what MK dir stands for is   make directory. And our directory is is a folder.  So now here, it's going to take in two arguments,   one is going to be the folder name that you want.  So I'm going to give it the value of tutorial. And   then we're going to pass in the callback with  an error. And we're just going to say if error,   console dot log error, oh, we successfully created  the folder so on so say, console, log folder   successfully created. So now if I was to  save this, and now before actually run this,   I'm just going to hit Ctrl. b. So you don't see  that there's any magic happening. So all I have   is my Node JS tutorial folder, and app.js file. So  now, if I go here, type node app, you can see that   we get the output a folder successfully created  and that our tutorials folder has been created.   Now let's say that I actually want to delete this  folder. So I'm just gonna hit Ctrl V again. And   this is actually going to give us an error, but  I'm just going to show you what the error is,   is basically going to complain that this folder  really exists. So I'm just going to say Fs that   are m, and r M stands for remove, and then dir and  that stands for remove folder. Now I'm going to   give the folder name, so we call it tutorial.  And this is also going to take a callback,   which gets an error. So now if I say if error,  console dot log the error, oh, we're gonna say   successfully deleted the folder successfully  deleted the folder. So now if I was to save this,   and now execute it, you see that we get an error  file already exists. And that's because the   tutorials folder already exists. And we're trying  to create another folder named the same thing. So   I'm just going to hit Ctrl V. Again, delete that  tutorial folder, I'm just going to hit delete,   confirm that Ctrl V again, let's execute this.  And you can see that we successfully deleted the   folder. So if I go up here, hit control B, you'll  see that it doesn't exist. So first thing we do is   we create a folder called tutorial. And then if  this is successful, then we're going to delete   the folder called tutorial. And you can see by  output that we successfully deleted the folder.   Now this is too fast. And that's why you wouldn't  be able to see it if we had the package manager   open. So now that we know how to create and delete  a folder, what I want to do now is create a folder   and then create a file within that folder. So I'm  just going to hit control B. And we can leave this   make directory. So we're going to make a folder  called tutorial. And if it's successful, it's   going to execute this else block. So let's remove  this. And then within here, we're going to create   our new file. So to do that, I'm just going to  say Fs dot write file. Now write file is going   to take in three arguments. It's going to take and  the name of the file, but in this case, we've got   to give it the full path. So I'm going to say dot  four slash. And what dot forward slash means is I   want you to start relative to App dot j s. And  then I want you to go inside the folder called   tutorial. So I'm just going to hit Ctrl B just to  show you. So app dot j s start here. There's going   to be a folder called tutorials. I'm going to go  in inside that folder, tutorial. And now I want   to you to create the file called example, dot txt.  So if I hit Control V again, and then the second   argument is going to be what the data that you  want, I'm just going to write 123 doesn't matter   for this example. And then the third argument is  it going to be a callback function which gets an   error. And then within here, I'm going to write if  error, console dot log the error onto the console.   Oh, we're gonna write successfully created, file,  successfully created file. So now let's save this.   So I'm just gonna hit Ctrl. S, down here, node  app. And you can see that it says successfully   created file down here. So now if I hit control B,  and I'm going to go up here and then hit control   B, you can see that we have our newly created  tutorial folder. And within here, we have our   example dot txt. So if we go in here, you can see  it has the data of one, two, and three. Now, what   I want to show you is, how would I delete a folder  that has a file within it. So you might be saying,   if I just go back here, hit Ctrl B, that can't  I just use Fs dot remove directory in order to   do this. Well, I am actually just going to comment  all this out. And what will end up happening if I   use the Remove directory function is that is that  I'll get an error. And the reason for that is,   because if I use the Remove directory function,  it has to be used on a directory or folder that   is empty. So just to show illustrate this,  that's going on right this quick remove   directory function. And if there's an error print  it else, we're just gonna print deleted folder. So   I'm just going to hit Ctrl S to save. And I'm  just going to type CLS to clear the terminal   node app. And you can see that we get an error  directory not empty, that we're trying to remove   a directory that has a file within it. So in order  to fix that, let's delete the file first. So I'm   just going to say Fs dot unlink. And the first  argument is going to be the file. So remember,   dot forward slash, and then we have to go into  the tutorials folder. And then I named the file   example dot txt. Next argument is going to  be a callback function which has an error,   I'm just going to say if error, print that out.  If there's no error, then what I want to do well,   if there's no error, that means that I  successfully deleted the file, which means   I can now successfully remove the file. So I'm  just going to copy this. And I'm going to put this   within the else block here. Add some semi colons.  And now if I was to save this, and now execute it,   you can see that we have deleted folder. And you  can see up here deleted from this. So if I go   hit control B, you can see that the folders been  successfully deleted. So what did we do? First,   we deleted the file that was within the folder.  And then if that was successful, then I wanted   to delete the folder itself. Last example that I  want to do is what happens when there are multiple   files within a folder, and you want to delete all  those files. So I'm going to cheat a little bit,   and we're just going to create it within our  package explorer. So I'm just gonna say new   folder, and we're gonna call it example. And I'm  just gonna give it two files. I'm just gonna say a   dot txt. And the second file is going to be b dot  txt. All right, so now I have my folder and I have   my two files. So how would I go about doing this?  Well, there's a method called Read directory. And   what read directory does is it gives you back the  list of files that you have within that folder. So   let's actually call it so I'm just gonna comment  on this out. comment this out. And then I'm just   going to type Fs dot read directory. Now the  first argument is going to be obviously the   name of the directory. And in this case, we call  it example. And then the second argument is going   to be a callback function. first parameter is  going to be error. And then second parameter   is going to have files now files is going to  be an array with the name of the file. So now,   we can test if there's an error, all we're gonna  do is print out the error, there is no error,   we're gonna print out files, I'm just gonna print  out files just to show you what files contains.   So if I save this, run this and the console,  you can see that we have our two files stored   within an array, a dot txt, and B dot txt. So now  let's actually loop through this array and delete   everything. So now I'm just going to say for let  file of files. And then within here, we can start   deleting each file individually. So I could say  Fs dot unlink. And then we're going to give it   the file name. So it's going to be dot forward  slash, example, then it's going to be the name   of the file. After that is going to take in an  argument callback for an error. And if there   was a problem deleting that file, it's going to  print it out to the console. If there wasn't,   we're just going to say, successfully deleted  file. So and So So, so successfully. deleted   file. So now if I was to save this, and now  execute this, you can see successfully deleted   file once twice. And if I hit Ctrl, B, you can  see that we have an empty folder called example.   In this tutorial, we're going to be talking about  the readable and writable screens. Now what these   screens allow us to do is basically be able to  read and write data more efficiently. And the   way that they accomplish this is by reading and  writing data, and chunks as opposed to reading and   writing the data all at once. So to get started,  we're going to have to require the FS module or   the file system module. So I'm just going to say  const. fs is equal to require Fs. Now that we have   our file system module included, we're going to  create a readable stream. And there's a method   called Fs dot create reach screen. And now I need  to give it the path. So if I just hit Ctrl, B,   you can see that I have an example dot txt file  here, and it has a bunch of texts that we're   going to be reading in. So if I head back to App  dot j, s, hit Ctrl V, again, we're just going to   give it the path of dot forward slash, example  dot txt. And then that's it. Now this is going   to return to us a readable stream. So I'm just  gonna save it within a variable. I'm just gonna   say cons reach stream is equal to Fs dot read  stream. And then here, what we can do is listen   for an event. Now the return object inherits  from the event emitter class. So that means we   could listen for events to occur. And one event  that we want to listen for is the data event. So   I'm just going to say read stream.on data. And  then this is going to take a callback function.   And now we're going to get a chunk of data and  return. So every time we read a piece of data,   this event data is going to be invoked. So this  callback function is going to be called every   time we get a piece of data. So now I'm just going  to print out the data onto the console. And you're   going to see why I call it a chunk and not the  full file in a second. So now if I save this,   go to node And you can see that we read this data  within two chunks. So we have to print out here,   we have a buffer here, and a buffer here. So  let's actually set the encoding type. So it's   a lot easier to what the sources, and we're just  going to set it to UTF, eight, and save this. And   now let's rerun this application. And there you  go, you see that we read our text file. So what   are the benefits are reading this in a chunk, as  opposed to loading the whole file? Well, for one,   when I get this chunk, I could immediately start  manipulating that chunk. So I don't have to wait   for the whole file to load in order to manipulate  it. Or let's say that I don't want to manipulate   this chunk of data that I got already, I want  to send it to a new file, well, I could start   sending that data to a new file, while I'm reading  in the data itself. So let's actually send it to a   new file. And for that, we're gonna have to create  a writable stream. So I'm just going to go here.   And I'm going to say const. Right stream is equal  to Fs dot create, write stream. And within here is   going to be the name of the file that I want to  write to. So I'm just going to call it example   two dot txt. And now within here, what I can do  is, instead of waiting to get the whole data,   I can start writing chunks to the new file.  So within here, instead of just printing out   console dot log, chunk, I can say, right stream  dot, right. And I could write this data to a new   file as I'm reading it. And so I could say chunk  here. And let's say that. And now if I run this   application node app. So now if I hit Ctrl, B, you  guys see our newly created file. And if I go here,   you can see that we wrote onto a new file. So  basically, what's happening here is I'm able to   write chunk by chunk, and our example two chunks,  in order to get the full file, I'm able to start   writing before the file is fully loaded. And  that's pretty much the power of using a stream.   This tutorial, I'm going to show you guys why you  should be using streams by trying to read a very,   very large text file. So to get started, I'm just  going to show you how big the file is. So I'm just   going to hit Ctrl. B, we have our large file dot  txt file here. And if I click review and explorer,   right click Properties, you can see that the size  it's about 2.7 gigs. So let's actually take a look   at what would happen if we were to use the read  file method from the file system module. So now,   if I was to execute this and type node app, you  see that we get an error and the error says file   size is greater than the possible buffer. Now,  what does that mean? Well, the read file uses a   buffer, but it uses a full buffer. Now what that  means is that I need at least 2.7 gigs in memory,   in order to load this file, because this file has  to be loaded, because this file has to fit within   the buffer. And it's saying, Hey, your buffer  size is just too small for this file. Now, I'm   just going to comment this out. And now what we're  going to use is a readable stream. So I'm just   going to comment this out. And then we're going to  uncomment this. And by the way, I have tutorials   on both readable streams and using the read file  method. So now I have the stream will look what   happens when I execute the code now. So if I was  to save this, and now execute it, you can see   that are readable stream has absolutely no problem  reading this file. So I'm just going to hit Ctrl C   to cancel this, because I don't want it to finish,  you know loading the entire thing. But why can   this be accomplished with streams but not using  this read file method? Well, one, a stream uses a   buffer awesome, but it doesn't use a full buffer.  It uses a very, very small buffer and what That   allows us to do is basically what's happening is  that you're ending out reading the file in chunks,   you're not reading the entire file at once. So  basically, every time a data event occurs, I am   getting a chunk of the file, I'm not attempting  to read the entire file at once. And therefore,   the buffer size could be a lot smaller, as opposed  to a read file method, which uses a full buffer,   which needs to be big enough to load the entire  file at once. And then server streams allow for   smaller buffer size, which is memory efficient.  And for data to be read and written and chunks.   And this tutorial, we're going to be going  over pipes. Now what a pipe allows us to   do is basically take a source stream, which is  just a readable stream, and send it over to his   destination, which is just a writable stream.  So in the last tutorial, we went over readable   streams and writable streams. And basically what  we did was create a read stream. And then from   there, we create a write stream. And then we  attached an event listener to the reach stream.   And every time we got a data event emitted, we  read a piece of the chunk from the read stream,   and then rewrote out that chunk to where we  wanted to send it. So there's actually a much   more simpler way. And the much more simpler way  is just to get rid of this. And all we're going to   do is say restream dot pipe. Now pipe is going to  take what restream gives us and it's going to pipe   it into our right stream. So now if I was to bring  up the terminal, and just type node app, and hit   Ctrl V, you can see we have our example Tex. And  then we created our example two dot txt. So the   pipe method is basically a shorthand version for  all that stuff that we wrote in the last tutorial.   So all we need to remember is, in order to use  a pipe, we need two streams, we need a source   stream. And we also need a destination stream.  In our case, the reach stream is our source,   this is the file that we want to read in, then  we call the pipe method on the retrieve. And then   this is going to take the destination where do we  want to send this data to, and that's to the right   stream. So now I want to talk about pipe chaining.  So let's give a more complicated example. And for   that, I'm going to bring in another module. And  I'm going to bring in Kant's z lib. Now z lib   is a module that is for basically compression,  compressing files, I'm just going to say require   z lib. Now what we're going to do is create a  transform stream. Now, what a transform stream is   basically is what it does is it takes the input.  So for example from our read stream, and then when   it receives that data, it manipulates that data  into something else. And in this case, what it's   gonna do is compress the data. So I'm just going  to create a transform stream. So I'm just gonna   say cons. Gs is equal to z lib dot create jesup  call that method. Now this is going to return   our transform screen. And now within here, a set  of saying reach dream, what I can do is send that   data that reach stream is giving us and I could  pipe it into our Gs. Now what GS is going to do   is take the chunks of data that is reading at a  time, and it's going to manipulate it and compress   it basically. So you're going to get a compressed  version of the read stream. And then from here,   we're going to pipe it out to our destination,  which is our right stream. So now if I was to   run this, let's save it. Now I'm just going to hit  Ctrl B. And if we go here to example, two dot txt,   you can see that we accidentally did not change  the type and that's my fault. So the type that   we're creating create write stream should not be  a txt file. It should be a.gz file and that's the   compression type. So I'm just going to save this  and let's run this application. Again. Now I'm   going to hit Ctrl B. And you can see that we get  an example two.txt.gz file. Now, if I clicked it,   it's going to say that Visual Studio Code cannot  open this. So I'm just going to right click it,   reveal an explorer. And you can see that zip  file is basically a compressed file. And I'm   going to double click it. And you can see that  our example two dot txt files here and with our   tax. So now let's give just one more example just  to get the hang of it, chaining pipes and using   a transform stream. So we saw what happens when  we compress the file and then write it. So let's   go and reverse, we're going to take our source,  which is compressed, we're going to uncompress it,   and then we're going to write it. So from here,  let's just go back to Visual Studio code. Let's   go back to App dot j s Ctrl V. And instead  of saying create jesup, what we want to do   is create unzip. So I'm just going to go here and  say create g unzip. And we're going to change this   variable to unzip. And now this is going to be our  transform stream. So I'm just going to copy this,   paste that here. And now what happened, well,  read stream has changed, right, so now I want   the compressed version of it. So let's go over  here, we're going to get rid of the encoding   type. The compressed file is called example  two dot txt Gz. So I'm just going to copy this,   I'm going to paste this in here. Now this input,  this reach stream is going to be piped to G unzip,   which is going to basically uncompress the  file, and then it's going to send it off to our   destination. So what do we want our destination to  be called, we could pretty much name this anything   you want. So I'm just gonna say uncompressed dot  txt. So now if I was to go ahead and save this   type node app, execute it, we hit Ctrl B. And  you can see that we have our uncompressed txt   file. So if I click this, you can see our example  Texas here, and that is successfully uncompressed.   In this tutorial, we're going to go over the HTTP  module. Now what the HTTP module allows us to do   is basically create a web server with node j s.  So to get started, we're gonna have to require   the HTTP module. So I'm just gonna say const.  HTTP is equal to require HTTP. Now from here,   we can call method called create server. And this  is going to give us a HTTP server object. So I'm   just going to say const server is equal to http  dot create server. Now, this method is going to   take a callback and this callback is going to give  us a request object as well as a response object.   So let's just do that. Now, the request object is  what the client requests from us. So for example,   if I am on Google Chrome, and I type in  www.google.com, I am requesting something   from Google. Now Google server is going to  take that request, and it's going to send me   a response back. So the most simplistic example  that I could give you is I could send a basic   text back to the client. So I could say rez, and  that's going to be my response, I'm going to say,   right, and I'm just going to pass in a string. So  I'm just going to say, Hello world, from node j,   s. Now within here, I haven't actually sent the  response back, I just told it what it is. So in   order to send the response, I'm going to say  res dot. And now this is going to take care of   our HTTP dot create server method. Now there's one  more thing that we have to do to get the server up   and running. And that's the total node j s. What  port that I want to listen for requests that song   is going to say server dot listen. And we're gonna  listen on port 3000. So now if I was to save this,   and now go down, Here type of node app, you can  see that our server is up and running. Now I'm   going to go to Chrome. And within here, I'm going  to type local host, colon, and then the port,   which we assigned was 3000. So that's where  we're listening for requests that if I hit Enter,   you can see that we get a response back  from the server, hello world, from node j,   s. So now from here, what we can do is actually  listen to requests, different routes. So let's   actually take a look at a property of the request  object. And one of the properties is called URL.   So instead of just saying, hello world, from node  j, s, I only want to say hello world from node j.   s, if it is the root domain, so I'm just gonna  say request dot URL is equal to forward slash,   then I'm gonna say res dot write Hello, world  from Node JS. And then don't forget that we   have to send the response back to the client.  So we're going to call resident and and now if   I was to save this, and we're going to is going  to hit Ctrl. C to kick us out of the server. And   then we're going to start the server back  up again. So we get our updated changes,   we're going to go back to Chrome, hit Enter. And  you can see that it works exactly the same. If we   were to add an else statement here. So let's  say they are not using the root domain, aka,   say rez dot write using some other domain, and  then we're going to send that out to the user. And   that's actually Ctrl. C this to stop the server.  And before we start up the server, I have to save   so I'm just gonna say Ctrl. S to save node app.  And now here, instead of localhost colon 3000.   I'm going to say local hosts, banana. And let's  see what response we get. And the response we get   back is using some other domain. Now this response  is going to be for anything we type because we   put it in the else block. So if I type that, I'm  going to get the same response. And then if I go   back and just have the forward slash, you can see  that we get the Hello World from node j s output.   And this tutorial, we're going to be going over  how we can serve static files, using the HTTP   and file system module. So to get started, I'm  just going to hit Ctrl. B to bring up the package   explorer. And you can see that we have a static  folder. And we have three static files. Now, these   files is a JSON file, an image, a PNG file, and an  index dot HTML file. So what I want to do is make   a request to the server and have the server send  these files back to me. So I'm just going to hit   Ctrl B to get rid of that. And the first thing  we're going to do is actually required modules   on this gonna say const, HTTP equal require HTTP.  And then our second module is going to be the file   system modules, I'm just gonna say require Fs.  Now, first step to do this is to actually create   the server. So I'm just gonna say HTTP dot create  server. And this is going to take a callback,   and we're gonna have a request object and a  response object. Now I'm going to call a method on   that server object. So I'm just going to say that  listen, and we're going to listen on port 3000.   Now, let's say that I want to read in a HTML file,  for instance. So let's go up here. And what I can   do is create a readable stream. So I'm just going  to say can't reach dream, it's going to be equal   to Fs. dot create, reach dream. And then within  here, we're going to pass in the path. So I'm   going to say dot forward slash, because it's going  to be relative to App dot j s. Now I need to go   inside the static folder. And then the name of the  file that I want read in is called index dot HTML.   Now what I want to do is actually write a header  for my response. Now what a header is responsible   for is the let the client know what kind of data  that I am expecting. So I'm just gonna say rez,   that right head. And then within here, we're  going to pass in the HTTP status code. So   I'm going to pass in 200. Now 200 means that  everything went okay with your request. And   then the second argument is going to be what the  content type, so I'm just going to hit content   type. And then we're gonna pass in text slash  HTML. All right, so now that we've written our   header, I'm just going to take you guys to Google  Chrome real quick just to look up the status   codes. Now you can see that HTTP 200 means that  the request has been successfully completed. So   whatever the user requested from the server, that  means everything went fine, as I said, and there's   a bunch of HTTP status code. So let's look at  another one. So another common one is four, four.   So you're going on a website, and you accidentally  Miss type the URL and they give you a not found   error. So that would be a 404 error. Now, let's go  back to our Visual Studio code. And let's complete   this, I'm just going to go down here. And within  here, I'm just going to pipe the reach stream into   where I want to send it. So I'm just going  to say reach stream dot pipe. And where do I   want to send this file, I want to send it to the  user. So I'm going to pass in rez, now read the   response object is also a writable stream. So I'm  piping it to the response object. So now I'm just   going to save this. Let's go back to Chrome. I'm  going to go here, Google, and I'm going to type   localhost 3000. And I should probably be noted  that you should start up your node applications,   I'm just gonna type node app. Now let's go back to  Google Chrome, hit refresh. And you can see that   our HTML file has been successfully sent. So let's  actually try to send the other static files. And   this was pretty much straightforward. So all we  have is if I hit Ctrl, B is an image and a JSON   file. So I'm just going to hit Ctrl V, again,  now all we need to do is obviously change the   file that we're reading in. So instead of index  dot HTML, let's do example dot JSON. Now I'm the   content type is obviously not a text slash HTML  file. So we're gonna have to pass in application   slash JSON. And now, if I was to save this, hit  Ctrl C, so we're going to restart the server, I'm   just going to clear out the terminal node app. Now  let's hit refresh. And you can see that our JSON   file gets loaded and sent to the client. Now let's  load up that image. So now the same exact thing,   I'm just going to hit Ctrl B, because I forgot  when I named the image, I named it example dot   png. So I'm just gonna change this to P and G. And  instead of application dot JSON, we're gonna just   gonna remove this. And we're just going to go here  and type image slash PNG. So now if I was to save   this, now, we got to restart the server Ctrl C to  cancel that out, no app. Now, if I go to Chrome,   hit refresh, you can see that my image has been  loaded. So that's basically the ins and outs   of how you would serve a static file using the  HTTP module, as well as the file system module.   In this tutorial, we're going to be going over  how we can create our package dot JSON file.   Now what the package dot JSON file is responsible  for is basically holding all our metadata for our   project, metadata being the name of the project,  the version number, etc. So to get started,   what we're going to use is called the node package  manager. So I'm just going to type NPM And then   I'm going to type in net, which means initialize,  I hit Enter. And you'll see that we get a bunch of   jargon. So what do we want to name, the package,  by default is going to be called the name of the   folder that you're currently in. So up here, you  can see no GS underscore tutorial. And it says the   default will be no GS slash tutorial. So I could  just hit enter, that's fine with me the version   number 1.0 dot zero, that's okay. Description.  So what is this package about? What is your   project about? And we're just gonna say tutorial,  because that's what we're using it for. And then   the entry point is pretty important. And it lets  us know which file should be used to start our   node application. So for example, if I was making  a website and uploaded to a server, it will let   the server know that that was our entry point  to our application. Test command. Let's ignore   that for now. Enter, and Git repository is pretty  self explanatory. Is it going to be your Git URL,   hit enter keywords, we're gonna leave that blank  as well. Author, go ahead and write down your   name. license is C as defined by me, then it's  gonna say Is this okay? And we're just gonna say,   yeah, that's fine. So you might think that  nothing has happened. But if I hit Ctrl, B,   you can see that we have our package dot JSON  file created. And if I take a look at this,   open it up, you can see that package dot JSON is  just a JSON file. And it has our configuration   setting. So the name, the version description of  our application, the entry point, scripts, author,   and license. And basically, in the next tutorial,  what we're going to end up doing is actually   going out and installing external packages  and including them within our own project.   This tutorial, we're going to be going over to  node package manager in order to install packages.   Now our package is is basically reusable code that  we can include within our own application, it's a   folder with one or more modules within it. So to  get started, we're actually gonna head over to   Chrome real quick. And there's actually a website  called NPM, J s.com. Now NPM, J s.com is where   we can actually look and discover new packages  that we can include within our application. So   I'm just going to pick out a package, and we're  going to install it and then use it. So I'm just   going to scroll down. And you could use the search  up here. Or, let's just pick a popular package.   So you can see packages that a lot of people are  installing. and scroll down more. And let's pick   lower das. And then here, we're given a bunch of  instructions. So it says in order to install this   package, I just have to type in this command NPM  i i in shorthand for install, and then the name of   the package. So in this case, the packages name is  lodash. So if I head back to Visual Studio code,   and I type NPM, install lodash. You can see that  it goes out, and it downloads the package for me   automatically. And now if I head back to my  package dot JSON file, the JSON file that we   created in the previous tutorial, you'll notice  that we have an extra property. And within this   property is called dependencies. And then it  gives us the name of the package we installed,   as well as the package version that we installed.  So now if I was just to hit Ctrl, B, you would see   that we have a extra folder and this extra folder  is called node modules. So if I opened this up,   you can see that our lodash installation is  stored here within this folder. So now this   is all fine and dandy, but how would I now  use lodash within my own personal project,   so I'm just going to hit Ctrl B. And we're going  to close out our package dot JSON file. And we're   going to go to App dot j s and basically what  we're going to do is require it so I'm just   gonna say cool. underscore is equal to require  lodash. And now from here, let's actually use   it to prove that this is working. So I'm just  going to say underscore dot fill. And fill is   basically going to take an array. So I'm just  going to pass in an array 12345. And the second   argument is going to take an A value, what do you  want to replace these numbers were, so I'm just   going to say banana. And the third argument is  going to be the start index. So what I want to   do is start at index one. And the last argument is  going to be the end index. And since we have five   elements within our array, the last index would  be four. So let's actually store this within a   variable. So I'm just going to say let example is  equal to that. And we're just going to print out   this onto the console. So I'm just going to hit  Ctrl S to save when I go to node. And you'll see   that we require lodash into our application. And  we've tested that one of the methods within lodash   is actually working. So we get a new array, and  we filled in index 123 with the value of banana.   And let's say that for whatever instance that you  installed the wrong module, or you want to get rid   of a module, so if I hit control B, and we're just  going to bring up the package dot JSON file and   hit Ctrl V again, what I can do is I can say  NPM, uninstaller, and then the package name,   which is going to be lodash. And you can see  that lodash is removed from our dependencies.   And if I hit Ctrl V, you can see that our node  underscore modules folder no longer exists.   And that's because we have no dependencies  that our application is using currently.   In this tutorial, we're going to be talking about  semantic versioning. Now, what semantic versioning   is, is basically just a standard that a lot of  Node JS packages follow and allows for us to   know what kind of changes have occurred, and the  updated version of the package. So to get started,   you can see that I have my package dot JSON  file open. And I have a dependency install   called lodash. Now within here, you see the  version of the package that I installed with   the carrot sign. And we'll talk about the carrot  sign within this tutorial as well. But for now,   I want you to focus on these three numbers. The  first number four is going to represent the major   version of this package, the second number is  going to represent the minor version. And the   third number is going to represent the patch  version. Now the major minor and patch numbers   all have different meanings. So for example, right  now, the latest version is four point 17 dot 11.   If I wake up tomorrow, and lodash is updated, and  it says the latest version is four point 17 dot   12. That means that that was a patch update. Now  all I patch update means is that they implemented   some bug fixes. Now likewise, same thing happens,  I go to sleep, they update lodash tomorrow,   and instead of four point 17 dot 11 is four point  18 dot 11. So that means that there was a minor   update. Now when a minor update does is it adds  new functionality. And it might deprecate some of   the old functionality, but you could still use it.  So it's a non breaking change update. And finally,   if I was to go to sleep tomorrow and wake up new  version of lodash is updated. And this time we   get version 5.0 dot zero. So what does that mean?  That means that there was a major update pushed   out to lodash. And what a major update indicates  is that there was a breaking change. So that means   version 5.0 dot zero is not compatible with the  code four point 17 dot 11 or any version of four.   So now let's talk about this carrot character. And  this carrot character was put there automatically   When we type NPM, install lodash. Now what this  carrot character symbolizes the following. So the   following rules, if you will. So this means  that whenever I use the carrot character,   that I do not want you to make any major  updates. So that means right now I'm on   version four as the major. But if there is a  minor update, or a patch update, go ahead and   download those new packages. Now, there's another  symbol called the tada symbol and total symbol is   right next to the number one on your keypad.  And that means that you want the following to   occur. That means you only want patch updates.  So let's say I'm on four point 17. Right now,   that means I only want you to change the last  number. So for example, if for Part 18 comes out,   this total symbol will say, hey, do not update  to that package. And last but not least, let's   say that you don't want the tilde or the carrot  sign up here. So for example, you don't want the   carrot sign to update the minor or the patch. And  you don't want the Tilda to just update the patch,   what you can do is remove the carrot or the  tilde a sign. And this guarantees that the   only version of lodash that you will ever have  within your package will be four point 17 dot 11.   In this tutorial, we're going to set up our first  Express server. Now all Express is is basically   a web framework for node j s. So in the previous  tutorials, we use the HTTP and file system module,   in order to serve static files. With Express,  however, you can see that we can accomplish   that and much more with much less code. So to get  started, I'm just going to go over to Chrome. And   here is Express jSs official website. So you  can see up here that they have guides for you,   you could reference the API. And basically, this  is just the documentation for Express. And you can   see that they give install instructions here. Now,  if you didn't go to the official website, or you   didn't know that they had an official website,  he probably would have went to NPM j s calm,   that Express is a publicly available package for  you to download and install. And you would have   just typed Express within the search bar here.  So I'm just going to head back to Visual Studio   code. And the first thing that we need to do is  actually create our package dot JSON. So I'm just   gonna say NPM and net, and I'm going to pass in  the flag, yes. Now, when you pass in the flag,   yes, you basically skip all these configuration  questions that they ask you when you type NPM. And   net. So now that we have our package, JSON, we can  actually install express itself. So I'm just going   to type npm install, express, you can see that  it's downloading right now. And now from here,   let's actually require Express JS into our  project. So I'm just gonna say const. Express   is equal to require Express. Now, when I require  this module, this Express module, what I'm getting   back is a function. So I'm just gonna call that  function. So I'm just gonna say Express. And this   function is going to return an object and this  object is going to have a bunch of methods that   we can use within our application. So let's store  this object within a variable. And by convention,   we will call that variable app. So I'm just going  to say app is equal to express. Now from here,   what I can do is call a method called get. Now the  first argument of get is going to take the route.   So we're just going to say forward slash. And then  the second argument is going to be the callback   function. And it's going to be request and  response. And then all we're going to do is say   res dot send. Hello, world. So this is going to be  our first application using Express. So when the   user visits the route forward slash, what we're  going to do is Sunday response of hello world   and that with a semi colon And then the last step  that we need to do is actually give it a port to   listen to. So I'm just gonna say app dot listen.  And we're just going to listen on port 3000. So   now if I was to save this type no app. And that's  going to run the server, head over to Chrome. Now,   I'm just going to open a new tab. And I'm just  going to type local host 3000. And there you   go. This is our first Express JS application.  And you can see that we got a response of hello   world. And in the upcoming tutorials, we're going  to dive deeper into the Express web framework.   In this tutorial, we're going to work more with  the HTTP GET requests. And we're going to be   talking about Curie string and route parameters.  So to get started, we created a basic Express   application from the previous tutorial. And we  gave it one route, which is basically the index   route, or you could refer to it as the homepage.  And we just said, Hello world. So if I was just   to run this node app, go to Chrome. Go to local  host. And we're going to put 3000, because that's   the port, and you see our basic route. So this  is the forward slash route. So now let's give   it a another route. So I'm just gonna go here, I'm  just gonna say app get. And we're going to give   it another route. And I'm just gonna say example.  And within here, we're gonna pass in a call back.   And now we're just going to say rez, that send  heading example, route. So now if I save this, I'm   just going to hit Ctrl. C to kick us out, we're  going to restart the server, so that it starts   with our newly saved file, head over to Chrome,  hit refresh, you see that our index page is still   working. And if I go here and type example, you  can see that we create another route, and that   it's hitting the example route now, as opposed  to the index route. So now let's go back here,   this is all fine and dandy. Now I want to talk  about Curie strings and route parameters. So I   want to start off with route parameters. And we're  going to create another route. So I'm just gonna   say app dot get. And I'm gonna say example. And  within here, I'm going to give it these colon, and   I'm just gonna say name. And that's going to be  the name of that route. And I'm just gonna say,   ah, and then the same exact thing. So I'm just  going to pass in a callback, I forget to add.   And then this time, what I want to do is access  from the request object. And I'm just going to say   params. And what we want to do is actually print  this out onto the console. Let's see what we get.   And the idea is that I want to get the value of  name. And ah, so we're just gonna say res dot   send. And we're just gonna say hitting, actually,  let's say example, with route params. So we're   just gonna save this, hit Ctrl C, I'm just going  to say CLS, no app, head over to Chrome. We're   going to hit refresh. So our examples working,  but now, we're going to pass information in so I'm   just going to pass in name. So Pedro and an age,  I'm going to put 99. So I'm going to hit Enter.   And you can see example with rope params has been  executed. So now if I take a look back at Visual   Studio code, you can see that when we hit this  route here, and we print out what's within our   request dot params, we get an object. And this  object contains the properties name and age,   and the values of Pedro and 99. So let's give a  more detailed example. Instead of just giving a   generic answer. I'm just gonna print send the  user back his name. So I say name plus Here,   I'm just going to say ah, and don't forget that  this name, property and age is within our requests   that params. And all request dot params is, is an  object. So I could say request dot params dot name   to access the name value. And I could say request  dot params dot age to access the age property.   So now if I save this, and we're going to reset  the server, CLS to clear the terminal node app,   head over to Chrome, hit refresh. And you can  see that we're sending back to the user Pedro in   99. And that we get the same output because we're  still printing it. So that's how we would get data   from the user using route parameters. But there's  also another type of data that you could send   back. And that's called Curie string parameters.  So what is that? Well, if I go back here,   and actually, let me just type this up, I'm going  to say console dot log. And again, we're going to   use the request object because the request object  is basically what the client is sending us. So I'm   just gonna say, request that Curie. And here in  Google Chrome, let's actually cancel this server.   I'm going to save this file, restart the server,  head over to Chrome. Just going to go up here,   hit refresh. Go back to Visual Studio code. And  you can see that we get an empty object. Now this   empty object is going to be our request, Curie.  So it's just a Curie string parameter. And the   reason it's an empty object is because we haven't  actually passed anything into it. So in order to   do that, there's going to go up here, we're going  to use a question mark. And then it's going to be   the name of the property that you want. So  I'm just going to make it up right now. I'm   going to give it a name of tutorial, and then  followed by an equal sign, and then the value   you want to assign it. So I'm just going to say  params. tutorial. And now if I hit Enter Here, you   can see that's pretty much the same thing that's  happening. But if I go back to Visual Studio code,   you can see that our request, Curie object is  no longer empty. We have a property of tutorial,   and we have params tutorial as a value. So now  let's say that I want to pass more than just   the tutorial. So how would I pass multiple query  string parameters. And if we head back to Chrome,   all we have to do is remember to start off with  a question mark, the name of the query string,   and then the value. So if you want to pass in a  second, curious string, what you can do is use   the Add sign or the app or stamp, whatever you  want to call it. And I'm just going to give it   sort. And then I'm just going to say equal. And  I'm going to give it the value of by age. And if   I hit Enter, head over to Visual Studio code. And  you can see now that when we print out our Curie   string, you can see that we get an object that  has tutorial. And it also has the property of   sort. So now you might be asking yourself, when  should I use a route parameter versus a query   string parameter, you should use route parameters  when you must have that data. So for example,   let's say name was an absolute must, I cannot have  a blank name. And I cannot have a blank age. So I   would use a route parameter. And let's say that I  want to give some optional settings. In that case,   I would use a query string parameter.  So for example, when we pass then sort,   we could be sorting the data by age,  and that would be an optional setting,   but I would need the name and the age to begin  with, so I would use a route parameter for that.   And if the user wants to sort the data, then  I will use a query string parameter for that.   In this tutorial, we're going to be talking  about serving static files using Express Now   what do I mean by a static file, I mean, your  HTML files, CSS, client side JavaScript, images,   videos, stuff like that. So to get started,  we're just going to require a path module,   and is basically a utility module that deals  with pass, just to make our lives a little bit   easier. And we're finished here, if I go  down here, I can say app not use now use,   whenever you see app use, it means that I'm using  middleware, the first argument is going to be the   alias for our static folder. So for example, if  I was to hit control B, you can see that I have   a static folder here. And what I want to do is  give this static folder, an alias, I don't want   people outside of my server to know that this  folder is called static. But let's take a look   inside of it. We have an index dot HTML, we have  example that j s. And we have a main dot CSS file,   just for an example. So now if I close that Ctrl  B, I'm going to call it public. That's going to   be the alias for my static folder. The second  argument is going to be a middleware function.   So I'm going to use a convenient method that  express provides us so I could say Express dot   static. And then I'm going to say path dot join.  Say dirname. R stands for directory name. Now,   dur name is a string. And this is going to give  us where app that j s is. So if we take a look,   by pressing Control B, is going to give us where  app dot j s is located. Now I want to go inside   to the static folder, because this is where all my  static assets are. So if I hit Control V, again,   we'll pass in as a second argument, the name  of the folder static. So I'm just going to end   this call in there says there's some error,  and I'm missing a parentheses. So now here,   instead of just saying hello world, let's actually  send a file. So I'm just going to remove this,   say res dot send a file. And we're going to use  our path module. Again, to make things easier.   I'm going to say path dot join, we're going to  give it the directory name that we're currently   in. We're going to go inside the static folder.  And then I want to serve the HTML file. So the   HTML file is called index dot HTML. So now, if  I was to save this, go down here, type node app.   Let's go over to Chrome. Now we're going to go  up here, type localhost 3000. And there you go,   you can see our static HTML file has been served.  If I type f 12. Let's take a look at the source   real quick. I can actually see it. And you can  see within our HTML file that we're using public.   Now remember, we don't actually have a folder  called public, we have a folder called static,   but to the client side is called public. And this  main dot CSS file. Now this main dot CSS file is   working, because you can see that our h1 tag is  red. And now if we go back down here, you can   see public j s and our example dot j s. And if  I go to console, you can see that I printed out   onto the console testing client side. So that's  basically the basics of serving static files   using Express. Now you can use this to use images  and videos, and it'll be the same exact process.   In this tutorial, we're going to be talking about  handling an HTTP POST request using Express. Now   an HTTP POST request is typically used when  working with forms. So I have my form set up   right here. I have an email address field and  a password field and if I was the hit submit,   that would be an example of a POST request. Now,  obviously, we're getting an error from node cannot   post to this route. And that's because we haven't  actually coded anything yet. So if we take a look   at Visual Studio code, you can see our form that I  set up, action is going to be the route that we're   going to code. So I just put forward slash, the  HTTP method is going to be a POST method. Here,   we see that we have our email field, and our  password field, and our button of type Submit.   So now I'm just going to head over to App j,  s. And I actually want to code the app dot POST   method. So if we take a look at our application of  this, it's currently All I have is an app dot get.   This is the route and I want doing is serving the  HTML file to the user. So in order to remedy this,   we're going to use a module that's going to parse  the form data for us. And that module is called   the body parser module. And that module is called  the body parser module. So to get started, we're   actually going to have to install this module.  So I'm just going to come down here, cancel our   server, I'm going to say NPM, install body parser.  So let that install. And now from here, what we're   going to do is require it into our application.  So I'm just going to say Kant's. Body parser is   equal to require body parser. And now from here,  what we're going to do is use middleware. So every   time we use middleware, we're going to call app  dot use. So here, I'm just gonna say app dot use,   then I'm gonna say body parser dot URL encoded.  And then within here, we're gonna pass in an   option called extended. And we're gonna set that  to false. So and that was the semi colon. And all   this is doing is allowing us to parse URL encoded  forms, it parses the data for us and attaches   it to the request body, the extended option is  set to false because we aren't dealing with any   complicated objects. All we want is an email and  password, which are both strings. So now that we   have that set up, let's actually code or app that  post HTTP requests. So we have our get here. And   now I'm just going to go down here. And instead of  saying app dot get, I'm going to say app dot post,   the first argument is going to be the route.  And as you saw on the HTML file, the action   route is the forward slash. The second argument is  going to be a callback function with the request   and rez object. And now from here, remember what  the body parser does, it parses the data for us,   and then attaches it to the body of the request  object. So now what I can do here is I could say   console dot log request dot body. And this is  going to give us an object with the properties   of email and password. And now from here, usually,  when you post something to the server, you usually   use whatever the user inputted, and you do some  database work. So I'm just gonna say database   work, here. And once that database work is done,  you assign a response or user. So I'm just gonna   say res dot send successfully, post that data.  Now, I'm just going to hit Ctrl S to save,   go down here, I'm going to type in Node app,  start up my server. Let's head over to Chrome.   And now if I hit refresh, just to reload it,  let's type some random email. Random password,   hit submit. So now what happened here was I filled  in my email and password I posted to the server,   I got a response back from the server saying  everything was posted successfully. So if I go   back to Visual Studio code, you can see that our  console dot log is working. We're printing out   the request dot body, and you can see that our  form data has been successfully parsed. So if we   take a look down here on to the console, you'll  see that we have an object With the property,   email and its value, and you also have property  of password and its value. So that's pretty much   how you would make an HTTP POST request  using Express and the body parser module.   In this tutorial, we're going to be talking about  how we can handle JSON data using Express and the   body parser module. So in the previous tutorial,  we talked about using the body parser module,   in order to handle URL encoded data. So what  we're going to do is take this form from the last   tutorial, and convert it to post JSON data. So to  get started, I'm just going to head over to Visual   Studio code. And right here, I have my  index dot HTML file and our form pulled up,   what I'm going to do is add an attribute to  the forum. So I'm just going to give it an ID,   and I'm going to call it form. And the reason for  that is I want to prevent the default submission,   I want to post data using jQuery Ajax. So that's  how we're going to post JSON data to our server.   So now that I have my ID, scroll down, and I  already put our jQuery CDN here, just to make   the tutorial a little bit quicker. And we're just  going to go here, and we're going to include our   script. So I'm just gonna say script. Now from  here, we're just gonna say document dot ready.   And the first thing that we want to do is get  our form. So I'm just say dollar sign, pound   sign form. And we're going to attach a submit  handler to our form. And this submit handler is   going to take a callback function, which has an  event as a parameter. So now, what I want to do   is prevent the default Submit. So we're just going  to take the event that we get, and we're going to   call prevent default. And from here, we're going  to use Ajax to actually make the POST requests.   And what we're going to do is post JSON data  back to the server. So I'm just going to say,   dollar sign, Ajax. And this is going to take a  bunch of configuration. So one of the properties   that we can use is called URL, and this is going  to be the endpoint that we're gonna have at our   server. So I'm just going to say forward slash,  second property is going to be type. And this is   going to be what kind of HTTP requests that we  want to make. And we're gonna post JSON to the   server. So I'm just gonna say post. third argument  is going to be the content type. And the content   type is obviously going to be JSON. So I'm just  gonna say application, slash JSON. Next property   that we're going to use is called data. And this  is going to be the actual form data that we want   to pass in. So how do we get the form data? Well,  I'm just going to say, get our form. And then I'm   going to serialize it using the serialize array.  And basically, this is going to take our form   data, so our email field and our password field  serialize it within an array. And this is going to   be a JavaScript array object. But remember, we're  posting JSON back to the server, because that's   the content type that we want. So we're just going  to say JSON that string of phi and pass in this   data as an argument. So this is going to take  the serialized array, and it's going to convert   it into JSON for us. Next, we're going to say  success. And success is going to be invoked when   we have successful response back from the server.  So I'm just going to say response. And we're just   going to print onto the console successfully.  Got response. And we're also going to print out   the response that we actually got from the server.  So once all this is done, let's scroll down a bit.   Everything looks good to me. So I'm just going to  save our index dot HTML file. We're going to head   back to app.js. So this is our server. And  down here, remember that we told our Express   application how to handle URL encoded data Now  what we need to do is just say app dot use body   parser. And this has a method called JSON. Now  this method is obviously going to parse JSON. And   it's going to attach it to our request dot body.  So now if I just put a semicolon there, and when   we scroll back down, you can see our original post  request is handled here. And what I'm going to do   is, instead of saying just plain text, we're gonna  respond back to the client using JSON. So I'm just   going to say, res dot JSON. And we're going to  pass an object. And we're just going to say that   it's been successfully posted. So now obviously,  what res dot Jason does is takes a JavaScript   object and converts it into JSON for us. So now  if I was to save this, and I'm just going to go   to terminal new terminal, and I'm going to say  node app to run the server, go back to Chrome,   when I type localhost. And now to test this  out, let's give it a dummy email and password,   click Submit. And now if I hit F 12, you can see  form serial array is not a function. So let's take   a look at this. And we're getting an error. Let's  actually take a look at that part of the code. And   that's because we did not include the dollar sign.  So let's include that now. Let's save it. Go over   to Chrome. Now we're going to hit refresh. And  type whatever we want. hit submit, go to console   and see that we successfully host that JSON to the  server. A server responded by posting this object   back to us. If I go back to Visual Studio code,  you can see that we have our serialized form data,   you can see that we have our serialized form  data. And that it's not JSON, that this is just an   array. And the reason why you're not getting back  JSON. And it's because our body parser module sees   that it's JSON and automatically converts it to  a JavaScript object. In this case, it's an array.   In this tutorial, we're going to be talking about  validating user input using joy. So what we're   going to do is validate the data coming in from  this form. Now, the reason you would validate user   input server side is because you can never trust  the data that you're receiving from the user. So   to get started, let's actually head over to Visual  Studio code. And I'm just going to cancel out our   server. And I'm going to type NPM, install joy.  And this is going to install the joy module. Now   from here, what we're going to do is actually  require it into our application. So I'm going   to go up here, I'm going to type const, Joy is  equal to require joy. So now that we have joy   in our application, let's actually go down to  our request. So we have our GET request, which   basically serves the form to our user. And we have  our post request, which is going to get the data   from our user. So from here, what we want to do  is actually validate the data that we get within   our request body. And in order to do that, what  we're going to do is create a schema. So what's   a schema, a schema is basically a blueprint,  a set of rules that we want our data to have.   So we have an email field, and we have a password  field. So what I want to do is make sure that the   email that the user gives me as a valid email, and  likewise with the password field. So what we can   do here is I can come down here, and we can create  a schema. Now remember, this is just a blueprint,   I'm going to say joy dot object. Now this is going  to give us a joy object. Next thing we need to do   is call a method called keys. Now keys is going to  work the same way that a regular JavaScript file   would work. You will have your key value pairs,  and we're going to pass in the options. Now within   here, what we want to do is set the rules that the  data that we're receiving must follow. So we have   a field called email. And within here, I'm gonna  say joy, I'm going to say string. So what I'm   saying is, the email field must be a string value,  I'm going to trim that data that I'm receiving,   I'm going to call a method called email. This is  going to check to see whether or not this is a   valid email. And I'm going to call one more method  called required. Now required does is if the user   sends me a no email, in other words, the user  doesn't fill out an email, I'm going to get an   error because this field is required. So let's  go back to our another property. And the next   property we have is password. So from here, I'm  going to do the same thing, joy, I need it to be   of type string. And let's change it up for the  password field. So let's say that I need the   password to be at least five characters. So I'm  going to call the min method and pass in five,   I'm going to call the max method. And I'm going to  pass in 10. So right now, this password must be a   minimum of five characters long, and a maximum  of 10 characters. So between five and 10. And   the last method I'm going to call is required.  And now let's end this with a semicolon. So now   that we have our blueprint, let's actually  use it. So we're going to call a method   called validate. So I'm just going to say joy dot  validate. And it's going to take three arguments,   the first argument is the object that you want to  validate. In this case, remember, we use the body   parser to parse the form data and attach it to the  body of the request object. So this is going to be   our first argument. The second argument is going  to be our blueprint, which we just created, it's   called schema. And our third argument is going to  be the callback function, that's going to take two   parameters. First one is going to be error, second  one is going to be result. And what we can do is   find out our result. So if I say if error, this is  going to execute true, if there's something wrong   with the data, so error is not know then this  code will be executed. So if error is executed,   we know something went wrong. So I'm just gonna  say res dot send, an error has occurred. But if   there is no error, what we can do is we could just  say res dot send. And I can say, successfully,   post that data. Now just for the sake of this  tutorial, I'm going to print out result, just so   you can see what the result is. Now, the result is  basically just going to be the data that we passed   in. So it's just going to be the request body. And  I'm going to go up here, and I'm going to print   out the error object. So now that I have these  two out, what we can do is get rid of our old   code from the last tutorial. I'm actually going to  save this, we're going to type in Node app. Let's   head over to Chrome. And from here, I'm just going  to type in, actually, let's just refresh the page   real quick. Let's type in an email. And let's  type in a password. And then if I hit submit,   you can see successfully posted data. So if I go  back to Visual Studio code, you can see that our   email is right here. And it probably hit Submit  twice because I probably clicked it twice. And   you can see that our result that's getting printed  out is just the request that body is whatever the   user posted. And you would do all your database  manipulation and calls here. So now let's actually   go back to Chrome. And this time, we're going to  type localhost again. And stead of giving valid   data. Let's see what happens when we post invalid  data. So I'm going to post valid data for email.   And for the password. Remember, we have to give  it between five and 10 characters long. So I'm   just going to give it two characters long and  let's see what happens. I'm going to hit submit.   And you can see the response we get an error has  occurred. So let's actually take a look at this   in Visual Studio code. You can see this big long  mess of mumbo jumbo So I'm just going to go back   up. And you can see the error that we're getting.  It says validation error child password fails,   because password must be at least five  characters long. So you can see our validation   is working. And this is pretty much the ins  and outs of validating user input using joy.   This is going to be part two of my joy  validation tutorial. So in this tutorial,   we're going to be covering how we can validate  a nested object, as well as how we can validate   an array. So to get started, I pretty much  stripped out all the Express stuff. And we're   going to simulate a user's requests. So for this  example, we have this user input, and it has a   nested object. And it has a property of personal  info with the properties of street address, city   and state. And we have preferences, which is going  to be our array, and you can see what values their   array contains here. So the first values that  we're going to start off with are string values,   and then we're going to move on to objects. So  the way that I'm going to tackle this problem is,   I'm going to look at our user input, and I'm going  to break it down into sections. So for example,   I'm going to develop a schema for personal  info, and then I'm going to develop a schema   for preferences. So to get started, we're going  to develop the personal info schema, first, I'm   just going to copy this, I'm going to come down  here. Now I'm gonna say Kant's, personal info,   and then I'm just gonna add schema. Next, I'm  going to create a joy object schema. So I'm just   gonna say joy dot object. Keys, we're gonna hit  enter a semi colon down here, we're going to go   up copy street address, would just develop a  schema like we normally would. So I'm just gonna   paste that street address is going to be joy dot  string, dot trim, I'm going to make this required,   we're going to do the same thing with the other  properties, go to city, copy this, go down here,   paste, and street address and city, we're going to  make the same exact thing. And last but not least,   we're going to take the state. And it's going to  be the same exact joy schema, except that we're   going to add that it has to be of length of two.  So I'm just going to copy this, paste this here.   And we're going to use the dot length method  and set that to two. So we're going for state   abbreviations. So now that we have our personal  info schema out of the way, let's develop a schema   for preferences. So I'm going to copy this, we're  going to go down here, I'm going to say Kant's,   preferences, schema. And this time, instead of  using joy dot object dot keys, we're going to say   joy dot array. And this is going to give us an  array schema. And we're going to use a helper   method called items. Now what items is going to  take in as an argument is basically any schema you   want. In this case, what we want is an array of  strings. So I'm just going to pass in the schema,   Joy dot string. So this is going to make sure  that all the items that within their array are   off strings. Last but not least, let's actually  combine these two to form one schema, I'm gonna   say Kant's schema. And I'm gonna say joy dot  object, dot keys, pass in this object. And this   time, we're going to say personal info. And that's  going to be equal to the schema we just created up   here. So we have our personal info schema. So I'm  just going to copy this, paste this here. And now   if I go back to my array, we call it preferences.  Copy that has this here. Preferences schema. Next,   let's actually call this so I'm going to go  down here, I'm going to say joy that validate   the first argument is going to be the same as last  tutorials. So we're just going to say user input.   second argument is the schema. So we're going  to use the built in schema Now that we made,   which consists of the two different schemas  that we created separately, last argument is   going to be the callback function. So I'll just  say error result. I'm going to say if error,   we're just going to print out what the error is.  Else, just print out the result. And the result is   just going to be the user input. So I'm just gonna  save this, let's actually add a semicolon here,   save this, we're gonna type in Node app. And you  can see that our data is validating. So the basic   premise is, if you're given a complicated  object, break them up into their individual   schemas. And then you could combine them like  so. Now I want to talk about, let's say that I   want an array of objects as opposed to an array  of strings. So we're just going to go up here,   we're going to change preferences to reference  array of objects. And then we have an example   object here. So this is a very simplistic example,  we just have a property of code example. And it   has the value of a string. So example, one, two,  and three. So we're just going to change this   through an array of objects. Let's go down here.  And instead of specifying joy dot string here,   because we're not looking for strings anymore.  We can say joy dot object, that keys and then   we just build our schema, like we did before.  So in this case, we only have one property,   it's called example. And we're gonna  give it the value of joy dot string,   dot required. So this was a very simplistic  example, if you had a more complicated object,   you would do the same thing like we've been doing.  So I'm just going to save this. And let's actually   execute this code, see if it's working node app.  And you can see that it validates, and we didn't   get any errors. So that's basically how you can  develop a schema for nested object, and how we   can develop schemas for arrays, and even create  our own custom schema objects for those arrays.   In this tutorial, we're going to be talking about  e j, s. Now what ej S is is a template language.   And that's going to allow us to write more dynamic  web pages. So to get started, what we have here is   a static HTML file, you can see that we have dummy  data here. So when it says you searched for stuff,   and we have search results of dummy data, now  what we want to do is use this HTML file as   a template that we can use for serving dynamic  data. So one way to do that is if we go back to   Visual Studio code, we can set the view of our  Express application. And in order to do that,   we would go here, and we could say, app  dot set is going to take into arguments,   we're going to specify the view engine, a second  argument is going to be the template that you   want to use. So we're just going to say e  j, s. Once we set the view engine to ej s,   we're going to have to hit Ctrl B. And we're going  to have to create a folder called views. And this   is going to store our E j s templates. So I'm just  going to go down here, right click New Folder,   and we're gonna call this views. Now Express is  going to automatically know that our templates   are located in the views folder, because that's  the default folder that looks for. So now if I   create my views folder, if I right click new file,  and instead of saying index dot HTML, I specify   index dot e j s. So now that I have my index.js  file, I'm just going to go to my index dot HTML.   I'm going to copy all this. And I'm just going to  paste the code within my index dot e j s. So now   I'm just going to save this. I'm going to go to  App dot j s. And what we do with templates is that   we've rendered on to the user. So I'm just going  to hit Ctrl B and get rid of the package explorer.   And instead of sending a static file, this is  going to remove this and now we're going to say   res dot render And then followed by the name of  the file that you run to render index. Now, you   do not need the specified a dot e j s on the side.  And that's because we already told express that we   are using ej s as the template. So now if I was  to save this, just gonna hit Ctrl C, node app,   head over to Chrome, we're going to hit refresh.  And you can see that we get the same exact output.   So what happened here? Well, when we render this  index.js file, what's happening is the server is   going to look at this E js file for e. js code,  it's going to execute it and then send back to the   client an HTML file. So now let's actually send  data to sun back to our E js file. So from here,   I'm just going to give us a route parameter,  I'm just going to say user query. And here we're   going to pass in an object. And this is going  to be the data that we want to display within   our index.js template. So now I'm just going  to give it a property. First, I'll say data,   then I'll give it a property of user query. And  then we're going to pass in request dot params dot   user query. So now if I save this, I'm just going  to hit Ctrl. C, just to exit out of our server.   Now we're going to go to our E js file. We're  gonna go here to our template. And now from here,   we're going to specify less than or sent sign  equal. What this means is I want you to output   onto the HTML file. Next, what we're going to do  is access the data that we just passed in. So how   did we do that? Well, we gave it the property  data, then we said, dot user query, afterwards,   we end it with percent sign, and then that. So now  this is gonna look at our app dot j s, it's gonna   say, Okay, I want to render the Index page. And  this is the data that I'm receiving. So we went to   data dot user query. So now if I was to save this  index.js template, let's start back to server,   no to app. Let's go to Chrome. Hit refresh. And  you'll see that we get cannot get forward slash.   And that's because we added a route parameter.  So let's say the user searched for books,   for example. Then it says, Hey, you search for  books. So imagine if this was a real website,   and we were on Amazon or eBay, you would do  a search. So then on top of that web page,   you would get Hey, you searched for books, you  searched for PCs, you search for whatever. So   that means I could use this ej s template for  all the items within my website. So now, let's   actually add some dummy data. So if I go back to  Visual Studio code, and what we're going to do   is instead of having hard coded stuff here,  when the user types in, we searched for books,   we're gonna display a bunch of books. So I'm just  going to go to App dot j s, we're going to pass   in more dummy data. So we have data user query,  we're gonna pass in another thing. And I'm just   going to give it a Enter key to make it fit on  one line. And we're going to pass in an array,   and this is going to be the search results.  search results. Pass in an array, and we're   just going to say, book one, book, two, and Book  Three. So now if I save this, go into my index,   e js file. Instead of saying dummy data, what we  can do is, we could go to data, because that's the   object that we're passing in. We're gonna say  search results. And then since it's an array,   we can access index zero. And this is going  to give us our first position. And remember,   since we this is an E JS template, we're going  to have to wrap this up within the following.   And now if I was to save this, let's go SQL Server  restarted up, go to Chrome, hit refresh. And you   can see that now we're dynamically populating the  web page. So now let's head back to Visual Studio   code. And what I want to do is, instead of just  outputting data that search results that index   zero data that search results index one, what we  can do is use a for each loop. So for example,   let's get rid of all this. And I started  with that, we're going to pass in less than   percent sign, we're going to get our array. So  what's our array at data, that search results, dot   for each, we get our result. And remember, we're  going to end this with a percent sign less than,   and the reason why we don't have an equal sign  here is because we are not outputting this onto   the HTML file. So for example, if I want to output  this equal sign, if you don't want to output it,   no equal sign. Next, within here, what we're  going to do is, we're going to display what   we want to output. So now what we're going  to do is use less than percent sign equal,   because we actually want this to output to  the HTML file. So I'm just gonna say, oh, II   result. And let's close our Li tag. So now we  have to end this. So we're just going to end   it with percent sign, we're not going to use the  equal sign because we do not want to output this   to the user. So now, if I was to save this, we can  go down here Ctrl C, node app, go to Chrome, hit   refresh. And you can see that our search results  gets dynamically added. So if we search for books,   and there was a million books, this code will work  for a million books. If we searched for iPhones,   and there was only three types of iPhones, this  code would work for three iPhones. So now let's   do an example involving conditionals.  So we're just going to give a simple if   statement. If the user is logged in, we want you  to display this, if the user is not logged in,   then we're not going to display anything extra.  So now if I go back to Visual Studio code,   let's write an if statement underneath our  h1 tag. So I'm just going to go here. I'm   gonna say this. If data logged in, and this is  going to be a Boolean containing true or false,   but and this here, and now the meat of our if  statement is going to be the HTML output that we   want to do. So now I'm just going to say h2. You  are logged and as data dot username and sent sign,   and then let's close our h2 tag. Now we have  to wrap up our if statement. So let's close   our if statement. And all we're going to do is  do the following ecgs. close our if statement.   And remember, we're not using the equal sign  because we're not wanting to output this. And   we're not using the equal sign up here because  we don't want to output this if statement. So   now if I was to save our index.js file, let's go  to App dot j s. And we're going to pass in those   properties that we added to our index.js file.  So we passed in logged in. And for this example,   we're just going to set true and the username is  going to be this. So I'm just going to go to index   that ETS just to see if we matched up properly.  Otherwise, we're going to get an error. logged in   username here. Make sure everything matches up.  Let's save this Ctrl C, node app. Head over to   Chrome, hit refresh. And you can see that since  we are logged in, we're displaying our h2 tag,   you are logged in as so. And so if we set that  to false, our h2 tag wouldn't appear. So that's   basically the ins and outs of how you can  use ej s within your Express application.   In this tutorial, we're going to be talking about  what middleware is, and how we can create our own   custom middleware. So middleware is basically the  code that gets executed between the user request   and the server itself. Now, in the previous  tutorials, we already used a middleware, and   that middleware was within the body parser module.  So if we take a look at our Express application,   on line five, we say app dot use, and then as  an argument, we pass an A function. And this   function is a middleware function, that when the  user makes a request, this function will take the   user's request and process it. In this case, the  body parser dot JSON function checks to see if   the user have sent any JSON data, processes that  and then attaches it to the request dot body. And   then it calls a function called next, to let the  server know that, hey, we're done processing this   request, you can send a nother request. So to  get started, we're just going to go down here,   I'm going to say app use. And then we're  going to pass in our own middleware function,   that's going to get executed whenever the user  makes a request. So this should be very familiar,   we're going to pass in the first parameter is  going to be the request object, their response.   And then the final parameter is going to be the  next method. So now we already are familiar with   the request object and the response object. So  what is this next method, this next method must be   invoked whenever you create a custom middleware.  So what the next method is responsible for,   is to let Express know that, hey, I'm finished  processing this request. If you do not call the   next method, what's going to end up happening  is you're going to timeout the server, because   it has no idea whether or not you're finished  processing that request or not. So right now,   I'm just going to say next, and we're just going  to call it. And to make things a little bit more   interesting. let's actually go up here. And  I am going to print out the request, that URL   and the request dot method. So now, if I was to  save this, let's actually restart the server,   I'm just gonna hit Ctrl. C, node app, we're going  to go to Chrome. I'm going to hit refresh. Now   when I hit refresh, what I did was make a get  request to the server. So let's actually take a   look at Visual Studio code to see what happened.  And you can see that our middleware is running.   So we made a request, it gives us the URL, it  gives us the method of the request. So we made a   get request when we hit refresh. And then we said  next, which let Express know that, hey, he's done   processing this. And then it got to this point  where we just sent res dot send middleware onto   the user. So that's why you see that we got this.  Now let's change this up. So instead of saying,   forward slash, because we got to get route there,  let's just make something up. Now, if I hit Enter,   you can see Can I get whatever this route is,  but that's okay, because we're not interested   in that. We're only interested in the middleware  for this tutorial. And you can see once again,   that our middleware is running fine. So  whenever there's a request made from the user,   this middleware function is going to get executed.  And you can see that our route was printed out.   And the type of request was also printed out onto  the console. Now, this is all fine and dandy. But   as we have it right now, whenever we use App dot  use, and we have our middleware, any user request   is going to get processed by this middleware.  Let's say that I only want this middleware to   execute when a certain route gets requested. So  right here, I'm just gonna go here, and I'm just   gonna say example. This is gonna be our route.  And now, whenever we call this example, route,   it could be any type of request, that could be  a get request, post request, put, elite, doesn't   matter, this middleware is going to execute. But  if it doesn't match this example route, then it's   not going to execute. So let's save this. And I'm  just gonna hit Ctrl, C, node app, start this up   again. And now I'm just gonna hit refresh. Go back  to Visual Studio code. And you can see that our   middleware is not executing. But if I go up here,  type example. Go back to Visual Studio code. And   you can see that our middleware is executing just  fine. And the last thing that you should note that   middleware functions can do is modify the request  object and the response object. So going back to   our body parser example, it parses the user's  request and searches for JSON, and then attaches   it to the request dot body. So to give a trivial  example, I can say take the user's request,   and I can add a property called banana. And I  could assign it the value of banana. And for the   sake of simplicity, since we already have this  route here, we're just going to get rid of all   this. And within our get route, we're just gonna  say, console dot log requests that been then. So   let's end that with a semicolon. Let's double  check everything. And this looks good. So I'm   just going to save this. And we're going to  restart the server. Now, the app, we're going to   go to Chrome. And we're going to hit our root. And  there we go. If we go back to Visual Studio code,   you can see what's going on here, we made a  request to the server, the server did some   processing the same thing that body parser did,  and then adds to the request object. And in this   case, we just added banana, gave it a value of  banana. And then here, when we got the request,   from our get route, you can see that we get the  output of banana. So that's pretty much the ins   and outs of how you can create your own custom  middleware, and how middleware works in general.   In this tutorial, we're going to be talking about  the Express router. Now what the Express router   allows us to do is separate our routes into  different files. This makes our code a lot more   manageable, as opposed to just sticking our routes  within the app dot j. s file. So to get started,   I'm just going to hit Ctrl B to bring up our  Explorer, I'm going to create a new folder to   store our routes. So I'm just going to right click  here, new folder. Let's call that routes. And   we're going to create a new file called people.  So this is where we're going to store our our   people routes. So I'm just going to hit Ctrl B  again. And since we're using the Express router,   we're obviously going to need to include the  Express module. So I'm just going to say const.   Express is equal to require Express. Next, we're  going to call Express dot router, which is a   method that's going to return to us a instance of  the router. So we're just going to say that within   a variable. So I'm just going to say Kant's route  is equal to express dot router. So now that we   have our router instance, what we can do is setup  our route. So we already know how to do that. So   I could say route back get. And we're just going  to give it the path. And we're going to give it   the callback. So the request object response. And  we're just going to say res dot send forward slash   being hit. Now let's just create a another row.  So I'm just gonna copy this. For example, and I'm   gonna call this example. And let's say example,  being hit. Now, we're not done yet. So right now   we have this route here. But how do we expose this  route so that our app.js file can access Well,   in order to do that, we're going to have to use  module dot exports. So I could go down here,   type module dot exports. And then we're just going  to export this route that we created. So now I'm   going to save this, we're going to head back to  our app.js file. And now down here, we're going   to have to actually require the people route. So  how do we do that? Well, I'm going to create a   variable called people. And we're just going to  require the file. So I'm just going to say dot   forward slash, I'm going to go inside the routes  folder. And then I'm going to include our people   file. But we're not done yet. Remember, on line  three, we created an express application. So now   we need to tell our Express application that  we want to use this people were out. So let's   go down here. I'm going to say app dot use. And  we're going to give it the base URL. So I'm just   going to say for slash people, and then we're  going to pass in the people route as the second   argument. So it's going to pass on people. So  now if I was to save this, head over down here,   node app, let's go to Chrome. And I type localhost  Port 3000. And that's because we do not have a   base URL. Remember, we gave it people. So this is  our base URL for this peoples row. So right now,   this forward slash would be accessed if I just  typed people at the end of localhost. So I'm   just gonna add that people. And now you can see  our four slashes being hit. And if I add another   forward slash, and do example, you can see our  example route is being hit. So now what happens   if you want to add middleware to these routes, so  I'm just going to go back to Visual Studio code,   we're going to go to our people route. And within  here, I could say route.us, and then pass in our   function, our middleware function that we want  to execute. So I could pass in my request object,   my rez, and next. And now I'm just gonna say,  console dot log middleware being used. Now when   I use route that use, all requests is going  to go through this middleware. So remember to   always call next, if you ever creating your own  custom middleware. And now if I was to save this,   let's hit Ctrl C, node app. When I go to  Chrome, hit refresh. And you can see that   our middleware is being used here. Now, this  middleware is only going to be used within our   people out. If we had another route here. Let's  say instead of people we had an animal route,   this middleware is obviously not going to  get executed because this middleware is   only specified to work with our people route.  So that's pretty much the ins and outs of how   you can use the Express router to actually  separate your routes from the app.js file.

Channel: freeCodeCamp.org

Views: 850,357

Keywords: nodejs tutorial, nodejs course, node, nodejs, node.js, javascript, js, node tutorial, node.js tutorial, web, web development, beginner, backend, server, node js, node js tutorial for beginners

Id: RLtyhwFtXQA

Length: 168min 43sec (10123 seconds)

Published: Tue Dec 04 2018