Functional JavaScript

Preface

What Is Underscore?

Underscore.js (hereafter called Underscore) is a JavaScript library supporting functional programming. The Underscore website describes the library as such:

Underscore is a utility-belt library for JavaScript that provides a lot of the functional programming support that you would expect in Prototype.js (or Ruby), but without extending any of the built-in JavaScript objects.

In case you didn’t grow up watching the kitschy old Batman television show, the term “utility belt” means that it provides a set of useful tools that will help you solve many common problems.^[1]

Getting Underscore

The Underscore website has the latest version of the library. You can download the source from the website and import it into the applicable project directories.

Using Underscore

Underscore can be added to your own projects in the same way you would add any other JavaScript library. However, there are a few points to make about how you interact with Underscore. First, by default Underscore defines a global object named _ that contains all of its functions. To call an Underscore function, you simply call it as a method on _, as shown in the following code:

_.times(4, function() { console.log("Major") });

// (console) Major
// (console) Major
// (console) Major
// (console) Major

Simple, no?

One thing that might not be so simple is if you already defined a global _ variable. In this case, Underscore provides a _.noConflict function that will rebind your old _ and return a reference ...