How to run JavaScript after the page has loaded

If you need to wait until your page loads before running some JavaScript, you should listen for DOMContentLoaded:

document.addEventListener("DOMContentLoaded", function() {
// your code here

The DOMContentLoaded event fires when the initial HTML document has been completely loaded and parsed, without waiting for stylesheets, images, and subframes to finish loading. — Mozilla Developer Center

In rare cases, you’ll need to wait until all the elements on your page have loaded entirely – meaning that your stylesheets, images, and subframes are finished loading. If that’s the case, you should listen for load. But in most cases, you should be using DOMContentLoaded instead.