The most popular library for a number of years has to be jQuery. jQuery was originally created by John Resig as a library to handle DOM manipulation and events. Cross-browser compatibility is a strong selling point for this library, since it works in everything from the newest version of Chrome to Internet Explorer versions so old they make most developers cringe. Its intuitive commands and functionality make it easy to pick up for novice developers. The library is so popular that, as of the end of 2013, it is estimated to be used in 61 percent of the top 100,000 websites in the world, according to the jQuery blog (http://blog.jquery.com/2014/01/13/the-state-of-jquery-2014/).

If you understand how jQuery works, you can skip the next section and go to Adding jQuery in our App. If not, here's a quick rundown on how jQuery works.