html - How to access css properties in javascript when applied via external CSS file?

Question

I have a little problem. When I set the css rule using some property, say, background-image in an external .css file and then try to access it using javascript in another external .js file, it does not work. That is to say I do not get any value for document.getElementById(someId).style.backgroundImage.

But when I set the css rule using style attribute in html file itself, it works.

So, my query is can't I access css property in js, if css is set in external .css file.

Answer 1

You can only access style properties in Javascript that have been set via Javascript (or the style attr).

To access the elements current style you should fetch the computed style of the element.

var el = document.getElementById('hello');
var comp = el.currentStyle || getComputedStyle(el, null);
alert( comp.backgroundColor );

Note, that the computed style may vary in browsers (like color being in hex or rgb) so you should normalize that if you want unified results.