Concatenate and Compress JavaScript with UglifyJS

The benefits of using something like RequireJS to asynchronously to load your project’s JavaScript was discussed previously. However, if you wish to load JavaScript in the more conventional way (that is, just sticking a script tag or tags in the browser) there are quick and lightweight ways to make this an efficient and viable option as well. These methods involve concatenating and compressing (minifying) your JavaScript files into one script file. At the end of the process you’ll only need to end up loading this one large script file (which is a lot quicker than loading numerous smaller scripts file) Additionally, if you concatenate your JavaScript files in a particular sequential order, you can easily make this a way to manage your dependencies… you just need to make sure that you load the dependency libraries before you load the libraries that require them. The tools we will look at in what follows makes this a fairly simple process.

To accomplish this in my workflow I use something called UglifyJS. It’s a simple package that runs in a Node.js environment. Node.js is a platform that allows you to run JavaScript system level applications on a server environment (or in this case, on our local machine). We can open our terminal and type something like “node myJavaScriptFile.js” and run some JavaScript we have written to do all kinds of neat stuff… all outside of the browser. So first things first, go and download and install Node.js if you haven’t already.

After that navigate to the directory where node is installed and run…

nmp (which stands for Node Package Manager, is a way of quickly installing the latest version of Node applications). You may have seen this elsewhere with Python’s pip command or Ruby’s gems. The -g parameter stands for global, which will enable you to run UglifyJS from anywhere on your machine.

Now what you can do is simply run the command according to the following format in the directory where your JavaScript files are…

In the example above, javascript-file1.js, javascript-file2.js, and javascript-file3.js will all be concatenated and compressed into a file named scripts.js file in the order in which they were set. So following this convention, you can load your dependencies where they are important in your JavaScript projects. Backbone.js, for example, has a hard dependency on Underscore. So you’d want to add Underscore *before* you’d add Backbone if you were doing a Backbone project. Also, a lot of times developers like to have jQuery available to them in their Backbone models, collections and views. So we could add jQuery into our list of files as well resulting in something like the following…

** Note that all of these files (underscore.js, jQuery.js, backbone.js) have to exist within the directory that you’re running the command from. scripts.js will be created if it doesn’t exist and overwritten if it does.

But whatever JavaScript you decide you need to include, all you have to do once the UglifyJS build process is complete is load the scripts.js file in your HTML. You can name this file whatever you want (it doesn’t have to be scripts.js). What I usually do in my workflow is set up a .bat file (and call it build-js.bat or something) that has all of my files and their dependencies set in the order that I need them. Then when I need to deploy my JavaScript to production I just run the .bat file.

So whichever way you choose to do it (either using the asynchronous module definition (AMD) pattern using something like RequireJS or using a tool like UglifyJS or using another similar solution) there are definitely good ways to load your handle your project’s JavaScript JavaScript in an efficient and effective manner.