Chrome extensions are usually based on javascript. Nowadays, jQuery is always used/though of when javascript is mentioned. Thus, it’s essential to know how to use jQuery – at least in the popup.

To get familiar with chrome extension development – check this out.

To trigger something when the page is loaded in javascript it’s usually the famous

$(document).ready(function(){
//whatever
});

This, unfortunately, will not work in the popup of your extension. Instead, I used another function

function ext_ready(){
//whatever
}

window.onload = ext_ready;

Ofcourse that is not my solution – but I read it somewhere long time ago that I forgot the resource. Probably it’s on stackoverflow somewhere.