Web/API/CSS/registerProperty

This is an experimental technologyCheck the Browser compatibility table carefully before using this in production.

The CSS.registerProperty() method registers custom properties, allowing for property type checking, default values, and properties that do or do not inherit their value.

Registering a custom property allows you to tell the browser how the custom property should behave; what are allowed types, whether the custom property inherits its value, and what the default value of the custom property is.

Syntax

CSS.registerProperty(PropertyDefinition);

Parameters

A PropertyDefinition dictionary object, which can contain the following members:

name: A DOMString indicating the name of the property being defined.
syntax Optional: A DOMString representing the expected syntax of the defined property. Defaults to "*".
inherits: A boolean value defining whether the defined property should be inherited (true), or not (false). Defaults to false.
initialValue Optional: A DOMString representing the initial value of the defined property.

Return value

undefined.

Exceptions

InvalidModificationError: The given name has already been registered.
SyntaxError: The given name isn't a valid custom property name (starts with two dashes, e.g. --foo).
TypeError: The required name and/or inherits dictionary members were not provided.

Examples

The following will register a custom property, --my-color, using registerProperty(), as a color, give it a default value, and have it not inherit its value:

window.CSS.registerProperty({
  name: '--my-color',
  syntax: '<color>',
  inherits: false,
  initialValue: '#c0ffee',
});

In this example, the custom property --my-color has been registered using the syntax <color> . We can now use that property to transition a gradient on hover or focus. Notice that with the registered property the transition works, but that it doesn't with the unregistered property!

.registered {
  --my-color: #c0ffee;
  background-image: linear-gradient(to right, #fff, var(--my-color));
  transition: --my-color 1s ease-in-out;
}

.registered:hover,
.registered:focus {
  --my-color: #b4d455;
}

.unregistered {
  --unregistered: #c0ffee;
  background-image: linear-gradient(to right, #fff, var(--unregistered));
  transition: --unregistered 1s ease-in-out;
}

.unregistered:hover,
.unregistered:focus {
  --unregistered: #b4d455;
}
button { 
  font-size: 3vw; 
}

We can add these styles to some buttons:

<button class="registered">Background Registered</button>
<button class="unregistered">Background Not Registered</button>

Specifications

Specification	Status	Comment
CSS Properties and Values API Level 1The definition of 'The registerProperty() function' in that specification.	Working Draft	Initial definition.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`registerProperty` Experimental'	Chrome Full support 78	Edge Full support 79	Firefox No support No	IE No support No	Opera Full support 65	Safari No support No	WebView Android Full support 78	Chrome Android Full support 78	Firefox Android No support No	Opera Android No support No	Safari iOS No support No	Samsung Internet Android Full support 12.0

Legend

Full support: Full support
No support: No support
Experimental. Expect behavior to change in the future.': Experimental. Expect behavior to change in the future.