CSSFunctionRule
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The CSSFunctionRule interface of the CSS Object Model represents CSS @function (custom function) at-rules.
Instance properties
This interface also inherits properties from CSSGroupingRule.
CSSFunctionRule.nameRead only Experimental-
Returns a string representing the custom function's name.
CSSFunctionRule.returnTypeRead only Experimental-
Returns a string representing the custom function's return type.
Instance methods
This interface also inherits methods from CSSGroupingRule.
CSSFunctionRule.getParameters()Experimental-
Returns an array of objects representing the custom function's parameters.
Examples
>Basic CSSFunctionRule usage
In this example, we define a CSS custom function and then access it using the CSSOM.
CSS
Our CSS defines a custom function using the @function at-rule. The function is called --lighter(), and outputs a lightened version of an input color. --lighter() accepts two parameters, a <color> and a <number>. It returns an oklch() color created using relative color syntax; the input color is transformed into an oklch() color and its lightness channel is increased by the input number.
@function --lighter(--color <color>, --lightness-adjust <number>: 0.2) returns
<color> {
result: oklch(from var(--color) calc(l + var(--lightness-adjust)) c h);
}
JavaScript
Our script starts by getting a reference to the stylesheet attached to our document using HTMLStyleElement.sheet, then getting a reference to the only rule in the stylesheet, the CSSFunctionRule — via CSSStylesheet.cssRules. We then log each of the CSSFunctionRule members to the console.
// Get a CSSFunctionRule
const cssFunc = document.getElementById("css-output").sheet.cssRules[0];
// Accessing CSSFunctionRule members
console.log(cssFunc.name);
console.log(cssFunc.returnType);
console.log(cssFunc.getParameters());
- The
nameproperty is equal to--lighter. - The
returnTypeproperty is equal to<color>. - The
getParameters()method returns an array that looks like so:js[ { name: "--color", type: "<color>" }, { defaultValue: "0.2", name: "--lightness-adjust", type: "<number>" }, ];
Specifications
| Specification |
|---|
| CSS Functions and Mixins Module> # the-function-interface> |