It’s super-common in front-end development to load a lot of content dynamically via AJAX. It’s tempting to rely on jQuery selectors to initialize these elements. We’ve all seen it: a huge chunk of code with twenty anonymous functions, each one a callback to a jQuery .each() method. We like jQuery selector callbacks because they’re convenient–no code is executed unless a match is found. It’s a built-in if-statement! But querying the DOM is an expensive operation which can slow down the loading of your site and drive away users.