Underscore: A Utility Belt for JavaScript - dummies

Underscore: A Utility Belt for JavaScript

By Chris Minnick, Eva Holland

Underscore is a collection of more than 100 useful JavaScript functions to help you get started and be more productive with JavaScript. To use Underscore’s functions on a web page, you need to include it using the script element. You can either include the library within the head element or load it right before the closing body tag in order to avoid blocking the loading of your web page while Underscore is loading.

Like any JavaScript library, you can either download Underscore and link to it on your own server or link to a hosted version. You can find a link to the latest version at http://cdnjs.com/libraries/underscore.js/.

To use Underscore’s functions after you’ve included the library, just preface the functions with an underscore and a period. For example, Underscore’s random function returns a random number between two numbers passed as arguments. The following statement will return a random number between 0 and 999:


Check out a complete list of functions provided by Underscore on the library’s website. Here are a few of the many useful functions.

Function What It Does
find Looks through the values in a list and returns the first one that passes a test.
filter Looks through the values in a list and returns an array of all the elements that pass a test.
sortBy Returns a sorted copy of a list.
countBy Sorts a list into groups and returns a count of the items in each group.
Pluck Extracts an array of values from an object or array.
max Extracts the largest value in a list.
min Extracts the smallest value in a list.
shuffle Returns a shuffled version of a list.
sample Returns a random sample of items from a list.

Once you get to know the functions in Underscore and start to use them, you’ll quickly understand why some people feel it’s the single most useful JavaScript library ever.