Introduction to Node JS1.pdf

Prepared By:
Prof. Bareen Shaikh
Department of Computer
Science,
MIT ACSC, ALNDI(D), PUNE

The following tools/SDK are required for
developing a Node.js application on any
platform.
 Node.js
 Node Package Manager (NPM)
 IDE (Integrated Development Environment) or
TextEditor
Note: NPM (Node Package Manager) is included in Node.js
installation

 Node.js files contain tasks that will be
executed on certain events
 A typical event is someone trying to access a
port on the server
 Node.js files must be initiated on the server
before having any effect
 Node.js files have extension ".js"

A Node.js application consists of the following
three important components −
 Import required modules − Use
the require directive to load Node.js modules.
 Create server − A server which will listen to
client's requests similar to Apache HTTP Server.
 Read request and return response − The server
created in an earlier step will read the HTTP
request made by the client which can be a
browser or a console and return the response.

 Step 1 - Import Required Module
We use the require directive to load the http
module and store the returned HTTP instance
into an http variable as follows −
var http = require("http");

 Step 2 - Create Server
Use the created http instance and
call http.createServer() method to create a
server instance
http.createServer(function (request,
response) {
response.writeHead(200, {'Content-Type':
'text/HTML});
response.end('Hello Worldn');
}).listen(8080);
console.log('Server running…”);

var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-
Type': 'text/html'});
res.end('Hello World!');
}).listen(8080);
Note:- create a filename.js file and type above program of “Hello World”
Save file at c:usersfoldername

 Open command prompt
C:usersfoldernamenode filename.js
Server running…
 Now here your computer works as a server
 Open browser in address bar type
https://localhost:8080

 Callback is an asynchronous equivalent for a function
 A callback function is called at the completion of a
given task
 All the APIs of Node are written in such a way that
they support callbacks.
For example
A function to read a file may start reading file and
return the control to the execution environment
immediately so that the next instruction can be
executed. Once file I/O is complete, it will call the
callback function while passing the callback function,
the content of the file as a parameter. So there is no
blocking or wait for File I/O.
 This makes Node.js highly scalable, as it can process
a high number of requests without waiting for any
function to return results.

 Create a input file filename.txt
 Write some content in it
 Create .js file
 Write following code in it
var fp = require(‘fs');
var data = fp.readFileSync(‘filename.txt');
console.log(data.toString());
console.log("Program Ended");
 Run the above node in command prompt.

 Create a input file filename.txt
 Write some content in it
 Create .js file
 Write following code in it
var fp = require(‘fp');
fp.readFile(‘filename.txt', function (err, data) {
if (err) return console.error(err);
console.log(data.toString()); });
console.log("Program Ended");
 Run the above node in command prompt.
 Program ended

Blocking Non Blocking
 program blocks reads
the file and then only
it proceeds to end the
program.
 blocking program
executes very much
in sequence.
 program does not wait
for file reading and
proceeds to print
"Program Ended" and at
the same time, the
program without
blocking continues
reading the file.
 non-blocking programs
do not execute in
sequence

Introduction to Node JS1.pdf

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