Javascript/Chrome extension how to run function?

Question

Hi

I try to make a extension for Google Chrome. But i have a problem. I can't get functions in the js file to run.

I tried to put a "alert('Hello World') inside the js file and it worked. But how do i start a function?

Have been searching and looking into the documents but i can't find anything. This is the javascript i try to run on a page to see if anything works:

if(document.getElementById('settingsboks')) {
    return false;
    }
        var div=document.createElement('div');
        div.id='settingsboks';
        div.style.padding='4px';
        div.style.border='2px solid #444';
        div.style.background='#fff';
        div.style.color='#000';
        div.style.float='right';
        div.style.width='300px';
        div.style.height='400px';