Learning JavaScript: Great libraries

After taking a look at JavaScript as a language we continue with some interesting and helpful libraries for web development.

After taking a look at JavaScript as a language we continue with some interesting and helpful libraries for web development.

underscore – going the functional route

What: Underscore has a lot of utility functions for helping with collections, arrays, objects, functions and even some templating.

How: Just a glimpse at the many, many functions provided (taken from the examples at underscorejs.org)

_.map([1, 2, 3], function(num){ return num * 3; });
=> [3, 6, 9]

_.map({one: 1, two: 2, three: 3}, function(num, key){ return num * 3; });
=> [3, 6, 9]

_.every([true, 1, null, 'yes'], _.identity);
=> false

_.groupBy([1.3, 2.1, 2.4], function(num){ return Math.floor(num); });
=> {1: [1.3], 2: [2.1, 2.4]}

_.escape('Curly, Larry & Moe');
=> "Curly, Larry & Moe"

var compiled = _.template("hello: <%= name %>");
compiled({name: 'moe'});
=> "hello: moe"

Why: JavaScript is a functional language but its standard libraries miss a lot of the functional goodies we are used to from other languages. Here underscore comes to the rescue.

when.js – lightweight concurrency

What: When.js is a lightweight implementation of the promise concurrency model.


var when = require('when');
var rest = require('rest');

when.reduce(when.map(getRemoteNumberList(), times10), sum)
    .done(function(result) {

function getRemoteNumberList() {
    // Get a remote array [1, 2, 3, 4, 5]
    return rest('http://example.com/numbers').then(JSON.parse);

function sum(x, y) { return x + y; }
function times10(x) {return x * 10; }

Why: Concurrency is hard. Callbacks can get out of hand pretty quickly even more so when they are nested. Promises make writing and reading concurrency code simpler.

require.js – modules (re)loaded

What: Require.js uses a common module format (AMD – Asynchronous Module Definition) and helps you loading them.

How: You include your module loading file as a data-main attribute on the script tag.

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

Inside your module loading file you define the modules you want to load and where they are located.

    baseUrl: 'js/lib',
    paths: {
        app: '../app'

requirejs(['jquery', 'canvas', 'app/sub'],
function   ($,        canvas,   sub) {
    //jQuery, canvas and the app/sub module are all
    //loaded and can be used here now.

Why: Your scripts need to be in modules, cleanly separated from each other. If you don’t have an asset pipeline want to load your modules asynchronously or just want to manage your modules from your JavaScript require.js is for you.

bower – packages managed

What: Bower lets you define your dependencies.

How: Just define a bower.json file and run bower install

	"name": "My project",
	"version": "0.1.0",
	"dependencies": {
		"jquery": "1.9",
		"underscore": "latest",
		"requirejs": "latest"

Why: Proper dependency management is a tough nut to crack and it is even harder to be pleasantly used (I am looking at you, maven).

grunt – the worker

What: Grunt is a task runner or build tool much like Java’s Ant.

How: Create a GruntFile and start automating:

module.exports = function(grunt) {

    pkg: grunt.file.readJSON('package.json'),
    uglify: {
      options: {
        banner: '/*! <%= pkg.name %> <%= grunt.template.today("yyyy-mm-dd") %> */\n'
      build: {
        src: 'src/<%= pkg.name %>.js',
        dest: 'build/<%= pkg.name %>.min.js'

  grunt.registerTask('default', ['uglify']);

Why: Repetitive tasks need to be automated. If you plan to use grunt and bower consider using yeoman which combines both into a workflow.

d3 – visualizations

What: d3 – data driven documents, a library for manipulating the DOM based on data using HTML, CSS and SVG.

How: There are many, many examples on d3js.org but to get a glimpse on how d3 works, here a small example.

Why: There are tons of chart or visualization libraries out there but d3 takes a more general approach. It defines a way of thinking, a way of manipulating the document based on data and data alone. It treats the DOM as part of your web application. Your visualization is a part of your document and not just a component you can forget about after creating it. This general approach allows you to create arbitrary visualizations not just charts.

last but not least: jQuery

What: jQuery is more of a collection of libraries then a single one, It features AJAX, effects, events, concurrency, DOM manipulation and general utility functions for collections, functions and objects.

How: Here we can just take a very quick overview because jQuery is so big.

// DOM querying and manipulation
$('.cssclass').each(function (index, element) {
  $(element).attr('name') = 'new name';

// AJAX calls
$.get('/blog/posts', function(data) {

// events
$( document ).ready(function() {
  console.log('DOM loaded');

// deferred objects aka promises
  function( status ) {
    // done
  function( status ) {
    // fail
  function( status ) {
    // progress

// utilities
var object = $.extend({}, object1, object2);

$('li').each(function(index) {
  console.log(index + ": " + $(this).text());

Why: jQuery is almost ubiquitous and this is not by chance. It provides a great foundation and helps in many common scenarios.


There are many more libraries out there and I would appreciate a pointer to a great library. This article can only give a short glimpse so please take a further look at their respective homepages. A word on testing or test runners: these will get an additional blog post.

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