To use a JavaScript library inside on of your pens, click the arrow in the upper right of the JavaScript editor to reveal it's options. Then click the box that says "No Library" which will reveal a dropdown menu to choose from.

This will load the latest version of that JavaScript library for your use. It's rather unlikely, but do note that we will always run the latest version of the JavaScript library, so if the library introduces a breaking change to one of their APIs, it will break your Pen as well (like real life!).

Note: You don't need to use DOM ready statements, like $(function() { }); in jQuery. The code will run after DOM ready automatically. If you need to wait for window load, you'll need to use something like $(window).load(function() { });