Global / Window

`window.getComputedStyle`

Returns an object containing the values of all CSS properties of an element after applying active stylesheets and resolving computations

Syntax

JavaScript

window.getComputedStyle(element, pseudoElt?)

Parameters

Parameter	Type	Description
element	Element	The element to get computed style for
pseudoElt	string	Optional pseudo-element string (e.g., '::before')

Return Value

A live CSSStyleDeclaration object with computed style values

Examples

Basic Usage

const el = document.querySelector('.box')!
const styles = window.getComputedStyle(el)
console.log(styles.color, styles.fontSize)

Practical Example

function getWidth(el: HTMLElement): number {
  const computed = window.getComputedStyle(el)
  return parseFloat(computed.width)
}

Advanced Usage

const el = document.querySelector('.tooltip')!
const before = window.getComputedStyle(el, '::before')
console.log(before.content)

Understanding window.getComputedStyle

The window.getComputedStyle method in JavaScript returns an object containing the values of all CSS properties of an element after applying active stylesheets and resolving computations. It belongs to the window object and is one of the most widely used methods for working with window values in modern JavaScript and TypeScript applications.

The method signature is window.getComputedStyle(element, pseudoElt?). It accepts 2 parameters: element, pseudoElt. When called, it returns a live cssstyledeclaration object with computed style values. Understanding when and how to use getComputedStyle() helps you write more expressive, readable code.

Common use cases for window.getComputedStyle include data transformation, input validation, API response processing, and building reusable utility functions. It works well alongside related methods like dom-style, dom-getboundingclientrect, dom-offsetwidth, enabling you to chain operations together for complex data manipulation pipelines.

Browser support for window.getComputedStyle is excellent across all modern browsers including Chrome, Firefox, Safari, and Edge. It is also fully supported in Node.js and Deno. For older environments, transpilation with Babel or a polyfill may be needed.