Here in chapter 12, I plan to match jQuery’s utility functions (https://api.jquery.com/category/utilities/) against the native APIs defined in the ECMAScript specification. Most of the code in this chapter will work both in the browser and on the server (with the notable exception of DOMParser and any references to window or document in examples). In modern browsers, jQuery is unnecessary most of the time. But even where jQuery saves a few keystrokes, it’s important to be able to roll your own utility function, even if you do choose to pull in a library for some of the more complex and lesser-supported features. After all, understanding how jQuery works its magic makes you a more complete and effective software developer.