Consider modules to be the same as JavaScript libraries.
A set of functions you want to include in your application.
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.
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);
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:
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"
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');
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:
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
If the response from the HTTP server is supposed to be displayed as HTML, you should include an HTTP header with the correct content type:
var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
res.write('Hello World!');
res.end();
}).listen(8080);
The first argument of the res.writeHead() method is the status code, 200 means that all is OK, the second argument is an object containing the response headers.
The function passed into the http.createServer() has a req argument that represents the request from the client, as an object (http.IncomingMessage object).
This object has a property called "url" which holds the part of the url that comes after the domain name:
demo_http_url.js
var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
res.write(req.url);
res.end();
}).listen(8080);
Save the code above in a file called "demo_http_url.js" and initiate the file:
Initiate demo_http_url.js:
C:\Users\Your Name>node demo_http_url.js
If you have followed the same steps on your computer, you should see two different results when opening these two addresses:
Will produce this result:
/summer
Will produce this result:
/winter
There are built-in modules to easily split the query string into readable parts, such as the URL module.
Split the query string into readable parts:
var http = require('http');
var url = require('url');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
var q = url.parse(req.url, true).query;
var txt = q.year + " " + q.month;
res.end(txt);
}).listen(8080);
Save the code above in a file called "demo_querystring.js" and initiate the file:
Initiate demo_querystring.js:
C:\Users\Your Name>node demo_querystring.js
The address:
http://localhost:8080/?year=2017&month=July
Will produce this result:
2017 July
Read more about the URL module in the Node.js URL Module chapter.
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:
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'
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:
I love the sun!
http://localhost:8080/winter.html
Will produce this result:
I love the snow!