Window.getDefaultComputedStyle()

getDefaultComputedStyle() gives the default computed values of all the CSS properties of an element, ignoring author styling.  That is, only user-agent and user styles are taken into account.

Syntax

var style = window.getDefaultComputedStyle(element[, pseudoElt]);

element

The Element for which to get the computed style.

pseudoElt Optional

A string specifying the pseudo-element to match. Must be null (or not specified) for regular elements.

The returned style is a CSSStyleDeclaration object.

Example

var elem1 = document.getElementById("elemId");
var style = window.getDefaultComputedStyle(elem1);

<style>
#elem-container {
   position: absolute;
   left:     100px;
   top:      200px;
   height:   100px;
 }
</style>
<div id="elem-container">dummy</div>
<div id="output"></div>  
<script>
    var elem = document.getElementById("elem-container");
    var theCSSprop = window.getDefaultComputedStyle(elem).position;
    document.getElementById("output").innerHTML = theCSSprop; // will output "static"
</script>   

Description

The returned object is of the same type as the object returned by getComputedStyle, but only takes into account user-agent and user rules.

Use with pseudo-elements

getDefaultComputedStyle can pull style info from pseudo-elements (for example, ::after, ::before).

<style>
 h3:after {
   content: ' rocks!';
 }
</style>
<h3>generated content</h3> 
<script>
  var h3       = document.querySelector('h3'), 
      result   = getDefaultComputedStyle(h3, ':after').content;
  console.log('the generated content is: ', result); // returns 'none'
</script>

Notes

The returned value is, in certain known cases, expressly incorrect by deliberate intent. In particular, to avoid the so called CSS History Leak security issue, browsers may expressly "lie" about the used value for a link and always return values as if a user has never visited the linked site, and/or limit the styles that can be applied using the :visited pseudo-selector. See http://blog.mozilla.com/security/2010/03/31/plugging-the-css-history-leak/ and http://hacks.mozilla.org/2010/03/privacy-related-changes-coming-to-css-vistited/ for details of the examples of how this is implemented.

Specifications

Proposed to the CSS working group.

Browser compatibility