Cài đặt request

Go to directory of your project

mkdir TestProject
cd TestProject

Make this directory a root of your project (this will create a default package.json file)

npm init --yes

Install required npm module and save it as a project dependency (it will appear in package.json)

npm install request --save

Create a test.js file in project directory with code from package example

var request = require('request');
request('http://www.google.com', function (error, response, body) {
  if (!error && response.statusCode == 200) {
    console.log(body); // Print the google web page.
  }
});

Your project directory should look like this

TestProject/
- node_modules/
- package.json
- test.js

Now just run node inside your project directory

node test.js

Node.js Events W3Schools

Node.js is perfect for event-driven applications.

---

Events in Node.js

Every action on a computer is an event. Like when a connection is made or a file is opened.
Objects in Node.js can fire events, like the readStream object fires events when opening and closing a file:

Example

var fs = require('fs');
var rs = fs.createReadStream('./demofile.txt');
rs.on('open', function () {
  console.log('The file is open');
});

---

Events Module

Node.js has a built-in module, called "Events", where you can create-, fire-, and listen for- your own events.
To include the built-in Events module use the require() method. In addition, all event properties and methods are an instance of an EventEmitter object. To be able to access these properties and methods, create an EventEmitter object:

var events = require('events');
var eventEmitter = new events.EventEmitter();

---

The EventEmitter Object

You can assign event handlers to your own events with the EventEmitter object.
In the example below we have created a function that will be executed when a "scream" event is fired.
To fire an event, use the emit() method.

Example

var events = require('events');
var eventEmitter = new events.EventEmitter();

//Create an event handler:var myEventHandler = function () {
  console.log('I hear a scream!');
}

//Assign the event handler to an event:eventEmitter.on('scream', myEventHandler);

//Fire the 'scream' event:eventEmitter.emit('scream');

Node.js NPM W3schools

What is NPM?

NPM is a package manager for Node.js packages, or modules if you like.
www.npmjs.com hosts thousands of free packages to download and use.
The NPM program is installed on your computer when you install Node.js

NPM is already ready to run on your computer!

---

What is a Package?

A package in Node.js contains all the files you need for a module.
Modules are JavaScript libraries you can include in your project.

---

Download a Package

Downloading a package is very easy.
Open the command line interface and tell NPM to download the package you want.
I want to download a package called "upper-case":

Download "upper-case":

C:\Users\Your Name>npm install upper-case

Now you have downloaded and installed your first package!
NPM creates a folder named "node_modules", where the package will be placed. All packages you install in the future will be placed in this folder.
My project now has a folder structure like this:
C:\Users\My Name\node_modules\upper-case

---

---

Using a Package

Once the package is installed, it is ready to use.
Include the "upper-case" package the same way you include any other module:

var uc = require('upper-case');

Create a Node.js file that will convert the output "Hello World!" into upper-case letters:

Example

var http = require('http');
var uc = require('upper-case');
http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write(uc("Hello World!"));
    res.end();
}).listen(8080);

Save the code above in a file called "demo_uppercase.js", and initiate the file:

Initiate demo_uppercase:

C:\Users\Your Name>node demo_uppercase.js

If you have followed the same steps on your computer, you will see the same result as the example: http://localhost:8080

Node.js URL Module W3schools

The Built-in URL Module

The URL module splits up a web address into readable parts.
To include the URL module, use the require() method:

var url = require('url');

Parse an address with the url.parse() method, and it will return a URL object with each part of the address as properties:

Example

Split a web address into readable parts:

var url = require('url');
var adr = 'http://localhost:8080/default.htm?year=2017&month=february';
var q = url.parse(adr, true);

console.log(q.host); //returns 'localhost:8080' console.log(q.pathname); //returns '/default.htm'console.log(q.search); //returns '?year=2017&month=february'
var qdata = q.query; //returns an object: { year: 2017, month: 'february' } console.log(qdata.month); //returns 'february'

---

Node.js File Server

Now we know how to parse the query string, and in the previous chapter we learned how to make Node.js behave as a file server. Let us combine the two, and serve the file requested by the client.
Create two html files and save them in the same folder as your node.js files.

summer.html

<!DOCTYPE html>
<html>
<body>
<h1>Summer</h1>
<p>I love the sun!</p>
</body>
</html>

winter.html

<!DOCTYPE html>
<html>
<body>
<h1>Winter</h1>
<p>I love the snow!</p>
</body>
</html>

---

---

Create a Node.js file that opens the requested file and returns the content to the client. If anything goes wrong, throw a 404 error:

demo_fileserver.js:

var http = require('http');
var url = require('url');
var fs = require('fs');

http.createServer(function (req, res) {
  var q = url.parse(req.url, true);
  var filename = "." + q.pathname;
  fs.readFile(filename, function(err, data) {
    if (err) {
      res.writeHead(404, {'Content-Type': 'text/html'});
      return res.end("404 Not Found");
    } 
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write(data);
    return res.end();
  });
}).listen(8080);

Remember to initiate the file:

Initiate demo_fileserver.js:

C:\Users\Your Name>node demo_fileserver.js

If you have followed the same steps on your computer, you should see two different results when opening these two addresses:
http://localhost:8080/summer.html

Will produce this result:

Summer

I love the sun!

http://localhost:8080/winter.html

Will produce this result:

Winter

I love the snow!

Node.js File System Module W3schools

---

Node.js as a File Server

The Node.js file system module allow you to work with the file system on your computer.
To include the File System module, use the require() method:

var fs = require('fs');

Common use for the File System module:

• Read files
• Create files
• Update files
• Delete files
• Rename files

---

Read Files

The fs.readFile() method is used to read files on your computer.
Assume we have the following HTML file (located in the same folder as Node.js):

demofile1.html

<html>
<body>
<h1>My Header</h1>
<p>My paragraph.</p>
</body>
</html>

Create a Node.js file that reads the HTML file, and return the content:

Example

var http = require('http');
var fs = require('fs');
http.createServer(function (req, res) {
  fs.readFile('demofile1.html', function(err, data) {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write(data);
    res.end();
  });
}).listen(8080);

Save the code above in a file called "demo_readfile.js", and initiate the file:

Initiate demo_readfile.js:

C:\Users\Your Name>node demo_readfile.js

If you have followed the same steps on your computer, you will see the same result as the example: http://localhost:8080

Node.js HTTP Module W3Schools

---

The Built-in HTTP Module

Node.js has a built-in module called HTTP, which allows Node.js to transfer data over the Hyper Text Transfer Protocol (HTTP).
To include the HTTP module, use the require() method:

var http = require('http');

---

Node.js as a Web Server

The HTTP module can create an HTTP server that listens to server ports and gives a response back to the client.
Use the createServer() method to create an HTTP server:

Example

var http = require('http');

//create a server object:http.createServer(function (req, res) {
  res.write('Hello World!'); //write a response to the client  res.end(); //end the response}).listen(8080); //the server object listens on port 8080

The function passed into the http.createServer() method, will be executed when someone tries to access the computer on port 8080.
Save the code above in a file called "demo_http.js", and initiate the file:

Initiate demo_http.js:

C:\Users\Your Name>node demo_http.js

If you have followed the same steps on your computer, you will see the same result as the example: http://localhost:8080

Node.js Modules W3schools

What is a Module in Node.js?

Consider modules to be the same as JavaScript libraries.
A set of functions you want to include in your application.

---

Built-in Modules

Node.js has a set of built-in modules which you can use without any further installation.
Look at our Built-in Modules Reference for a complete list of modules.

---

Include Modules

To include a module, use the require() function with the name of the module:

var http = require('http');

Now your application has access to the HTTP module, and is able to create a server:

http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.end('Hello World!');
}).listen(8080);

---

Create Your Own Modules

You can create your own modules, and easily include them in your applications.
The following example creates a module that returns a date and time object:

Example

Create a module that returns the current date and time:

exports.myDateTime = function () {
    return Date();
};

Use the exports keyword to make properties and methods available outside the module file.
Save the code above in a file called "myfirstmodule.js"

---

---

Include Your Own Module

Now you can include and use the module in any of your Node.js files.

Example

Use the module "myfirstmodule" in a Node.js file:

var http = require('http');
var dt = require('./myfirstmodule');
http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write("The date and time are currently: " + dt.myDateTime());
    res.end();
}).listen(8080);

Notice that we use ./ to locate the module, that means that the module is located in the same folder as the Node.js file.
Save the code above in a file called "demo_module.js", and initiate the file:

Initiate demo_module.js:

C:\Users\Your Name>node demo_module.js

If you have followed the same steps on your computer, you will see the same result as the example: http://localhost:8080