Optimize your JavaScript with RequireJS

RequireJS is an effective way to improve the speed and quality of your JavaScript code additionally making it a lot more readable and easier to maintain.

In this article I’ll introduce you to RequireJS and how you can begin using it. We will go through requiring files and defining a module and even touch on optimization.

In simple terms require.js is a script loader that allows you to slip your JavaScript code into files and modules thus managing the dependencies of each model.

Requiring Files

To start working with RequireJS and its Asynchronous Module Definition (AMD) we must first downloadit, then link to the require.js file in the head of our document like so:

<script src="require.js" data-main="main"></script>

You may be wondering what that data-main attribute is, well using RequireJS means that when you call require in the head of your document you are also linking to the main file of your JavaScript application, the data-main attribute is a link to the main JavaScript file for your application, in this case main.js. (Note that RequireJS automatically adds the .js at the end of the filename.)

In this main.js file you will place the configuration for RequireJS, load in your modules and define a base path for use when requiring files.

The Require Function

RequireJS uses a simple require function to load in scripts, in this example RequireJS loads jQuery:

require(["jquery"], function($) {
  return $(‘#mydiv”).html(‘Hello this is RequireJS talking”);
});

One of the best things about RequireJS is that it is extremely readable, if you look at that block of code you will see that first require grabs the file with the name of jquery.js and it passes an anonymous function with jQuery’s $ as a parameter, when that is done you are free to use all the JQuery code you please.

Now, you normally wouldn’t have the jQuery library in a file named jquery.js, as with most plugins and frameworks, we normally choose to load then from their GitHub or the Google CDN, and for that we need to configure the paths so that they point to the right place:

require.config({
 paths: {
   "jquery": "https://ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js"
 }
});

This means you can require jQuery via Google and use it without a problem. (Note that I’ve used the name “jquery” in this example, but you could call it anything you like.)

Defining a module

Using the AMD pattern means that our code can be structured in modules; these models are just bits of code that do something in our application. You can place two lines of code in a module or 100, it just depends on what you want that module to do.

To define a module we use code like this:

define(function () { 
 function add (x,y) {
   return x + y;
 }
});

In this example I have created a simple add function with no dependencies, but if this function needed jQuery to work properly, the define function would be structured like this:

define([‘jquery’], function () { 
 function place(mydiv) {
 return $(mydiv).html(‘My Sample Text’);
 }
});

Using this syntax we tell JavaScript to go get jQuery first, and then run the code so that jQuery is available when needed. We can also use this in modules we have written in JavaScript files, it’s not limited to frameworks or plugins.

Optimization

As you can see RequireJS is a great tool for organizing your files into modules and only loading what you need. The downside is that too many JavaScript files result in poor load times, which is why RequireJS includes an optimizer to collect the data from all the files and place it in a single minimized file.

All in all, RequireJS is one of the best ways to organize and optimize your JavaScript for the modern web.