The Window.getComputedStyle() method returns an object containing the values of all CSS properties of an element, after applying active stylesheets and resolving any basic computation those values may contain. Individual CSS property values are accessed through APIs provided by the object, or by indexing with CSS property names.

Syntax

var style = window.getComputedStyle(element [, pseudoElt]);
element
The Element for which to get the computed style.
pseudoElt Optional
A string specifying the pseudo-element to match. Omitted (or null) for real elements.

The returned style is a live CSSStyleDeclaration object, which updates automatically when the element's styles are changed.

Examples

In this example we style a <p> element, then retrieve those styles using getComputedStyle(), and print them into the text content of the <p>.

HTML

<p>Hello</p>

CSS

p {
  width: 400px;
  margin: 0 auto;
  padding: 20px;
  font: 2rem/2 sans-serif;
  text-align: center;
  background: purple;
  color: white;
}

JavaScript

let para = document.querySelector('p');
let compStyles = window.getComputedStyle(para);
para.textContent = 'My computed font-size is ' +
    compStyles.getPropertyValue('font-size') +
    ',\nand my computed line-height is ' +
    compStyles.getPropertyValue('line-height') +
    '.';

Result

Description

The returned object is the same CSSStyleDeclaration type as the object returned from the element's style property. However, the two objects have different purposes:

  • The object from getComputedStyle is read-only, and should be used to inspect the element's style — including those set by a <style> element or an external stylesheet.
  • The element.style object should be used to set styles on that element, or inspect styles directly added to it from JavaScript manipulation or the global style attribute.

The first argument must be an Element. Non-Elements, like a #text Node, will throw an error.

defaultView

In many code samples, getComputedStyle is used from the document.defaultView object. In nearly all cases, this is needless, as getComputedStyle exists on the window object as well. It's likely the defaultView pattern was a combination of folks not wanting to write a testing spec for window and making an API that was also usable in Java.

Use with pseudo-elements

getComputedStyle can pull style info from pseudo-elements (such as ::after, ::before, ::marker, ::line-marker — see the psuedo-element spec).

<style>
  h3::after {
    content: ' rocks!';
  }
</style>

<h3>Generated content</h3> 

<script>
  var h3 = document.querySelector('h3'); 
  var result = getComputedStyle(h3, ':after').content;

  console.log('the generated content is: ', result); // returns ' rocks!'
</script>

Notes

  • The returned CSSStyleDeclaration object contains active values for CSS property longhand names. For example, border-bottom-width instead of the border-width and border shorthand property names. It is safest to query values with only longhand names like font-size. Shorthand names like font will not work with most browsers.
  • CSS property values may be accessed using the getPropertyValue(propName) API or by indexing directly into the object such as obj['z-index'] or obj.zIndex.
  • The values returned by getComputedStyle are resolved values. These are usually the same as CSS 2.1’s computed values, but for some older properties like width, height, or padding, they are instead the same as used values. Originally, CSS 2.0 defined the computed values as the "ready to be used" final values of properties after cascading and inheritance, but CSS 2.1 redefined them as pre-layout, and used values as post-layout. For CSS 2.0 properties, getComputedStyle returns the old meaning of computed values, now called used values. An example difference between pre- and post-layout values includes the resolution of percentages for width or height, as those will be replaced by their pixel equivalent only for used values.
  • Returned values are sometimes deliberately inaccurate. To avoid the “CSS History Leak” security issue, browsers may lie about the computed styles for a visited link, returning values as if the user never visited the linked URL. See Plugging the CSS History Leak and Privacy-related changes coming to CSS :visited for examples of how this is implemented.
  • During CSS transitions, getComputedStyle returns the original property value in Firefox, but the final property value in WebKit.
  • In Firefox, properties with the value auto return the used value, not the value auto. So if you apply top:auto and bottom:0 on an element with height:30px and a containing block of height:100px, Firefox's computed style for top returns 70px, as 100 − 30 = 70.

Specifications

Specification Status Comment
CSS Object Model (CSSOM)
The definition of 'getComputedStyle()' in that specification.
Working Draft  
Document Object Model (DOM) Level 2 Style Specification
The definition of 'getComputedStyle()' in that specification.
Obsolete Initial definition

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Basic supportChrome Full support YesEdge Full support YesFirefox Full support Yes
Notes
Full support Yes
Notes
Notes Before version 62 this function returned null when called on a Window with no presentation (e.g. an iframe with display: none; set). Since 62 it returns a CSSStyleDeclaration object with length 0, containing empty strings (bug 1467722; also see bug 1471231 for further work).
IE Full support 9Opera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support Yes
Notes
Full support Yes
Notes
Notes Before version 62 this function returned null when called on a Window with no presentation (e.g. an iframe with display: none; set). Since 62 it returns a CSSStyleDeclaration object with length 0, containing empty strings (bug 1467722; also see bug 1471231 for further work).
Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android ?
Pseudo-element supportChrome Full support YesEdge ? Firefox Full support YesIE Full support 9Opera Full support 15Safari Full support YesWebView Android ? Chrome Android ? Edge Mobile ? Firefox Android ? Opera Android ? Safari iOS ? Samsung Internet Android Full support Yes

Legend

Full support  
Full support
Compatibility unknown  
Compatibility unknown
See implementation notes.
See implementation notes.

See also