This document provides an introduction to NodeJS and examples of using modules in NodeJS applications. It discusses using the require function to load modules, the order NodeJS searches for modules, and examples of core NodeJS modules and third party modules. It also provides examples of using synchronous and asynchronous filesystem operations to read files and print output.

1. NodeJS by examples

2. Understanding require
• Foo.js
• circle.js (in the same folder)
var circle = require('./circle.js');
console.log( 'The area of a circle of radius 4 is '
+ circle.area(4));
var PI = Math.PI;
exports.area = function (r) {
return PI * r * r;
};
exports.circumference = function (r) {
return 2 * PI * r;
};

3. Node core modules
• The core modules are defined in node's source
in the lib/ folder.
• They are always given a preference in loading.
This means that you should never name you
file with the same name as that of the inbuild
module.

4. Pecking order of loading modules*
• If the file at '/home/ry/projects/foo.js' called
require('bar.js'), then node would look in the
following locations, in this order:
• /home/ry/projects/node_modules/bar.js
• /home/ry/node_modules/bar.js
• /home/node_modules/bar.js
• /node_modules/bar.js
• *Source: http://nodejs.org/docs/v0.4.2/api/modules.html

5. Pre-requisite
• Install NodeJS from https://nodejs.org/
• Node –v to check if node is already installed.
• Pick you favorite editor (I am experimenting
with Microsoft Visual Code)

6. Examples from
• Learnyounode:
https://github.com/workshopper/learnyouno
de

7. NodeJS by example
• Problem 1: HelloWorld.js

8. • console.log("HELLO WORLD");
Solution

9. Sync call on console
• Write a program that uses a single
synchronous filesystem operation to read a
file and print the number of newlines (n) it
contains to the console (stdout)

10. Hint
• require('fs')
• process.argv[2]
• readFileSync

11. Async call on console
• Write a program that uses a single
asynchronous filesystem operation to read a
file and print the number of newlines it
contains to the console (stdout)

12. Hint
• require('fs')
• readdir