Using The DOM Ready Event

One of the great advantages of using a library like jQuery is that is provides functions like ready() so you can activate your JavaScript code when the DOM is ready, and not when everything has been loaded. This can be significantly earlier, especially if you an image heavy page.

The ready() function is quite chunky, and has to account for a variety of browsers and versions. However, if you know you are running on a recent browser, you can always look at hooking directly into the DOMContentLoaded event. This is part of the HTML5 spec.

To use it you need to add an event listener using the document.addEventListener method. This takes two parameters, the name of the event – in this case DOMContentLoaded, and a callback function to call when the event is triggered.

document.addEventListener("DOMContentLoaded", function domready() {
  document.removeEventListener("DOMContentLoaded", domready);
  console.log("DOM Ready");

Notice how I have given the function a name – domready(), this is so I can unhook the function from the event listener once the event has fired.