The document discusses key concepts in Node.js including modules, using Node.js as a web server with HTTP, managing NPM packages, the event loop, event emitters, and streams/pipes. Modules allow code reuse and sharing functionality. Node.js can be used as a web server by creating an HTTP server to handle requests and responses. NPM is used to install, update, search for, and uninstall third-party packages. The event loop handles asynchronous events and callbacks in Node.js. Event emitters emit and handle events. Streams allow reading/writing files and piping data between streams.

1. Objective
What is Modules?
How to use Node js as Webserver using HTTP?
How to manage NPM third party packages?
What is Event Loop?
What is Event Emitters?
Node js Streams and pipes

2. What is Modules?
 Node.js provides a few core modules out of the
box to help you access files on the file system,
create HTTP and TCP/UDP servers, and perform
other useful functions.
the module.exports property or the exports object allows a module to select what should be shared with the
application

3. How to use Node js as Webserver
using HTTP?

4. HTTP Request and Response:
var http=require('http')
var
server=http.createServer((function(request,response)
{
response.writeHead(200,
{"Content-Type" : "text/plain"});
response.end("Hello Worldn");
}));
server.listen(7000);
Now, your computer works as a server! If anyone tries to
access your computer on port 7000, they will get a "Hello
World!" message in return!
http://192.168.102.84:7001/

5. How to manage NPM third party
packages?
1. To install package:
npm install express –global
The global option in the above statement is what allows
the modules to be installed at a global level.
2. Listing global package:
npm list –global
3. To Install a specific version of a package
npm install underscore@1.7.0

6. Basic Commands
4. To update a package version
npm update underscore
5. To search particular package
npm search express
6. To uninstall package
npm uninstall express

7. What is Event Loop?
Event loop makes Node JS as Event driven programming capable.
The Event Loop is technically not available inside Node JS.
Node JS is a single threaded process but you can use the
concurrent process with events and callbacks which improve the
performance.

8. Event Emitters
Event Emitter is the class which handles the event looping.
// Imports events module
var events = require ('events');
// EventEmitter object
var eventEmitter = new events.EventEmitter ();
For One time event handlers
eventEmitter.once('<methodname>', function() {
console.log(‘<message>’);
});

9. Example

10. Node js Streams
Node makes extensive use of streams as a data transfer
mechanism.
1. Read from the file
2. Write in the file
3. Pipes
Read and Write streams can be piped together using the
pipe() method in node js, which takes two arguments:
1. A Required writable stream that acts as the
destination for the data
2. An optional object used to pass in options.