Adrian Chia
3 min read#nodejs#express

Getting Started on NodeJS

What is NodeJS?

NodeJS is a server side, event-driven, non-blocking IO JavaScript platform that helps create lightweight, fast and efficient applications

What can I do with NodeJS?

Virtually anything! For example:

How do I get start?

Make sure that you have NodeJS installed, you can download it from http://nodejs.org. Once you can it installed, check that you can run it from your command prompt / terminal via the following command:

Terminal window
node --version

There are two important files/directories we need to know about:

  1. package.json file
  2. node_modules directory

package.json

The package.json file stores metadata/information about your project. It typically has the following content

{
  "name": "project-name",
  "version": "1.0.0",
  "description": "Project description",
  "author": "Your Name <[email protected]>"
  "private": true,
  "main": "main.js",
  "dependencies": {}
}
  • Name - the name of your project (required)
  • version - the version of your project (required)
  • description - additional information about your project (optional)
  • author - author of this project, typically in author <email> pair, you can also use {"name":"Your Name", "email":"[email protected]"}
  • private - we do not want to publish this project to npm registry.
  • main - the main entry point of your project. You can create a .js file with any name as your entry point and put the file name here.
  • dependencies - dependencies or libraries that the project is going to use.

For more information about package.json file, visit http://browsenpm.org/package.json

node_modules

The node_modules stores downloaded project dependencies for your project. It can be project specific dependencies, which only usable in the same project, or global dependencies, which can be used in multiple projects.

The dependencies are usually published and downloaded from a registry. The default is https://www.npmjs.org

Creating a Web Application Project

Create an empty directory for your project, you can name it anything you want, let’s call it MyProject for now. Enter into the directory and create a file called package.json and another file called main.js. The package.json file describes information about your project and is very important especially if your project depends on third party modules.

In your package.json file add the following content

{
  "name": "myproject",
  "version": "1.0.0",
  "description": "NodeJS example",
  "author": "Your Name <[email protected]>"
  "private": true,
  "main": "main.js",
  "dependencies": {}
}

Next, in your command prompt / terminal, execute the following command in MyProject directory:

Terminal window
npm install express --save

This will download and install a dependencies called express, which is a light weight web application framework, and stored in node_modules folder. For more information about express, visit http://expressjs.com/

The command above will also append the dependency in the package.json file. You can also specify the dependency manually in the package.json file and execute just the npm install part to install the dependency.

Next, we will write our main application code in the main.js file. Add the following content to the main.js file:

var express = require('express');
var app = express();


app.get('/',function(req,res){
    res.send('hello world');
});


app.listen(3000);

Let’s explain the code above:

var express = require('express'); means that we import our dependencies, which in this case is express

var app = express() means that we create our Express based application in a variable call app

app.get('/hello',function(req,res){
    res.send('hello world');
});

means that when we visit http: / /<hostname or localhost>:<port>/hello it will print hello world

app.listen(3000); means that we run the application and listen to port 3000. You can also specify the hostname as second argument, such as app.listen(3000,'example.com')

Lastly, executed the following command and visit http://localhost:3000/hello from your browser and see your application in action!

In Summary

We have learnt what NodeJS is, what it is capable of, some of the important files/directories and how to create a NodeJS based application with Express framework.