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CSS: registerProperty() static method

files/en-us/web/api/css/registerproperty_static/index.md

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{{APIRef("CSSOM")}}

The CSS.registerProperty() static 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 types are allowed, whether the custom property inherits its value, and what the default value of the custom property is.

Syntax

js-nolint
CSS.registerProperty(propertyDefinition)

Parameters

  • propertyDefinition
    • : An object containing the following properties:
      • name
        • : A string representing the {{cssxref("dashed-ident")}} name of the property being defined.
      • syntax {{optional_inline}}
        • : A string representing the expected syntax of the defined property. Defaults to "*". See the {{cssxref("@property/syntax", "syntax")}}.
      • inherits
        • : A boolean value defining whether the defined property should be inherited (true), or not (false). Defaults to false.
      • initialValue {{optional_inline}}
        • : A string representing the initial value of the defined property.

Return value

undefined.

Exceptions

  • InvalidModificationError {{domxref("DOMException")}}
    • : The given name has already been registered.
  • SyntaxError {{domxref("DOMException")}}
    • : The given name isn't a valid custom property name (starts with two dashes, e.g., --foo).
  • {{jsxref("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:

js
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 it doesn't work with the unregistered property!

css
.registered {
  --my-color: #c0ffee;
  background-image: linear-gradient(to right, white, 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, white, 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:

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

{{EmbedLiveSample("Examples", 320, 320)}}

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also