Why is document.querySelector not working on pseudo element?

Question

I am playing with pseudo elements and javascript but some how i can not style it using javascript.

    var div = document.querySelector(":before");
    div.style["display"] ="none";

div{
    width:200px;
    height:200px;
    background:red;
    position:relative;
}

div:before{
    position:absolute;
    content:'';
    top:0;
    right:-100px;
    width:100px;
    height:100%;
    background:green;
}

<div></div>

do anyone knows why this is not working?

Answer 1

If you want to style pseudo elements from javascript you have to use the CSSOM to inject the rules. It's not trivial, but it's possible.

var sheet = document.styleSheets[0]; //get style sheet somehow
var rules = sheet.rules; 
sheet.insertRule('div:before { display: none; }', rules.length);

a slightly modified example from this article

CCSOM Reference