1.JQuery

First released in 2006, jQuery is very much the grand old man of JavaScript libraries, and remains an essential piece of kit to this day. You’ll find it chugging away under the hood of WordPress itself, and across innumerable other projects that power the modern web. It’s also explicitly backed by some of the biggest names in the business.

From a budding JavaScript developer’s point of view, the promise of jQuery is nicely summed up in its tagline – “write less, do more.” Start diving into it and you’ll get an elegant way of handling the DOM, along with a natural introduction to the wider JavaScript front end ecosystem in the form of jQuery UI, jQuery Mobile, Sizzle, and QUnit.

2.Numeral.js

Formatting and manipulating numbers is at the heart of a huge amount of day-to-day programming tasks, and the Numeral.js library does an excellent job of making that substantially simpler in JavaScript. Not only does it make life easier for developers who are new to the language, it’s also an admirable example of a library that tackles one problem well. It’s definitely one to add to the toolkit as soon as possible.

3.Retina.js

Continuing our theme of practical libraries with obvious everyday utility, Retina.js is both a front end workhorse and practical way of easing into using JavaScript libraries on personal projects.

We’re living in an increasingly high-definition world these days. Sites of all stripes need to be able to handle retina devices gracefully, while not forcing unnecessarily large images on everyone else – Retina.js gives you an easily understandable way of doing just that.

4.D3.js

Having gotten numbers firmly under control with Numeral.js, you’ll eventually be looking to do some fancy things with data generally. That’s where D3.js comes in. D3 enables you to create data-driven documents to your heart’s content in a way that’s truly compatible with web standards.

As even a quick look at the project’s list of examples shows, this has a huge range of practical uses across all manner of projects. Start diving into the impressive list of associated tutorials, and you’ll soon be confidently displaying data with just a few lines of code.

5.Backbone.js

Full-fledged JavaScript frameworks such as Angular and Ember attract a lot of the headlines, but there’s a huge amount to be said for beginning with Backbone when you’re just getting to grips with JavaScript. It’s an easy route into the concept of models and views in JavaScript, supported by great documentation and tutorials, and a great way of starting to explore the power of the REST API in WordPress to boot.

6.Chai.Js

Testing is a topic that should always be at the front of any responsible developer’s mind, and it’s just as true in JavaScript as it is in any other language – perhaps even more so given the bewildering number of devices and scenarios where it’s deployed. If you’re just starting with the topic and have a few dollars to spare, it’s hard to beat James Shore’s Lets Code: Test-Driven JavaScript series.

7.ReactJs

We’ve deliberately left the newest library for last. With its groundbreaking approach to thinking about modern UIs, Facebook’s React library has caught the attention of developers worldwide, the team at Automatic being among them, but it’s not necessarily the easiest programming paradigm to get your head around.

Scotch.io’s intro to the library is an excellent starting point, and Andrew Farmer’s list of tutorial recommendations provides plenty of material for further exploration – Build With React is a particularly notable resource that he identifies.