CSSStyleDeclaration: setProperty() method

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨July 2015⁩.

The CSSStyleDeclaration.setProperty() method interface sets a new value for a property on a CSS style declaration object.

Syntax

setProperty(propertyName, value)
setProperty(propertyName, value, priority)

Parameters

propertyName

A string representing the CSS property name (hyphen case) to be modified.

value Optional

A string containing the new property value. If not specified, treated as the empty string. A null value is treated the same as the empty string ("").

Note: value must not contain "!important", that should be set using the priority parameter.

priority Optional

A string allowing the CSS priority to be set to important. Only the values listed below are accepted:

"important" (case-insensitive) for setting the property as !important;
"", undefined, or null for removing the !important flag if present.

Anything else causes the method to return early and no change to happen (unless value is empty, in which case the property is removed regardless of the priority value). false, for example, is not a valid priority value.

Return value

None (undefined).

Exceptions

NoModificationAllowedError DOMException: Thrown if the property or declaration block is read only.

Alternative usage

If priority can be omitted, JavaScript has a special simpler syntax for setting a CSS property on a style declaration object:

style.cssPropertyName = "value";

Examples

Setting the box properties

In this example we have three buttons, which can be pressed to dynamically alter our box paragraph's border, background color, and text color to random values (see the live example at the end of this section).

The MDN live sample infrastructure combines all the CSS blocks in the example into a single inline style with the id css-output, so we first use document.getElementById() to find that sheet.

We then loop through the different rules contained inside the stylesheet in the array found at stylesheet.cssRules. For each rule we check whether its CSSStyleRule.selectorText is equal to the selector .box p, which is the one we want.

If so, we store a reference to this CSSStyleRule object in a variable. We then use three functions to generate random values for the properties in question, and update the rule with these values. In each case, this is done with the setProperty() method, for example boxParaRule.style.setProperty('border', newBorder);.

HTML

html

<div class="controls">
  <button class="border">Border</button>
  <button class="bgcolor">Background</button>
  <button class="color">Text</button>
</div>
<div class="box">
  <p>Box</p>
</div>

CSS

css

html {
  background: orange;
  font-family: sans-serif;
  height: 100%;
}

body {
  height: inherit;
  width: 80%;
  min-width: 500px;
  max-width: 1000px;
  margin: 0 auto;
}

.controls {
  display: flex;
  justify-content: space-around;
  align-items: center;
}

div button {
  flex: 1;
  margin: 20px;
  height: 30px;
  line-height: 30px;
}

.box {
  display: flex;
  justify-content: center;
  align-items: center;
  height: calc(100% - 70px);
}

.box p {
  width: 50%;
  text-align: center;
  font-weight: bold;
  font-size: 40px;
  height: 150px;
  line-height: 150px;
  background: red;
  border: 5px solid purple;
  color: white;
  transition: all 1s;
}

JavaScript

const borderBtn = document.querySelector(".border");
const bgColorBtn = document.querySelector(".bgcolor");
const colorBtn = document.querySelector(".color");
const box = document.querySelector(".box");

function random(min, max) {
  const num = Math.floor(Math.random() * (max - min)) + min;
  return num;
}

function randomColor() {
  return `rgb(${random(0, 255)} ${random(0, 255)} ${random(0, 255)})`;
}

// Find the inline stylesheet generated for MDN live samples
const stylesheet = document.getElementById("css-output").sheet;

const boxParaRule = [...stylesheet.cssRules].find(
  (r) => r.selectorText === ".box p",
);

function setRandomBorder() {
  const newBorder = `${random(1, 50)}px solid ${randomColor()}`;
  boxParaRule.style.setProperty("border", newBorder);
}

function setRandomBgColor() {
  const newBgColor = randomColor();
  boxParaRule.style.setProperty("background-color", newBgColor);
}

function setRandomColor() {
  const newColor = randomColor();
  boxParaRule.style.setProperty("color", newColor);
}

borderBtn.addEventListener("click", setRandomBorder);
bgColorBtn.addEventListener("click", setRandomBgColor);
colorBtn.addEventListener("click", setRandomColor);

Result

Specifications

Specification
CSS Object Model (CSSOM) # dom-cssstyledeclaration-setproperty

Browser compatibility

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This page was last modified on ⁨Oct 17, 2025⁩ by MDN contributors.

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