Notes

Point 1. node.js example

//Load HTTP module
var http = require("http");

//Create HTTP server and listen on port 8000 for requests
http.createServer(function (request, response) {

// Set the response HTTP header with HTTP status and Content type
response.writeHead(200, {'Content-Type': 'text/plain'});

// Send the response body "Hello World"
response.end('Hello Worldn');
}).listen(8000);

// Print URL for accessing server
console.log('Server running at http://127.0.0.1:8000/')


point 2. express example
line1 var express = require('express');
line1 var app = express();

line1 app.get('/', function (req, res) {
line1 res.send('Hello World!');
line1 });

line1 app.listen(3000, function () {
line1 console.log('Example app listening on port 3000!');
line1 });

-->first 2 line
var express = require('express');
=> Requires the Express module just as you require other modules and and puts it in a variable.

var app = express();
=> Calls the express function "express()" and puts new Express application inside the app variable (to start a new Express application). It's something like you are creating an object of a class. Where "express()" is just like class and app is it's newly created object.

point 3. To make objects available outside of a module==>
you just need to assign them to the exports object. For example, the square.js module below is a file that exports area() and perimeter() methods:

exports.area = function (width) { return width * width; };
exports.perimeter = function (width) { return 4 * width; };

We can import this module using require(), and then call the exported method(s) as shown:

var square = require('./square'); // Here we require() the name of the file without the (optional) .js file extension
console.log('The area of a square with a width of 4 is ' + square.area(4))