KeyframeEffect: pseudoElement property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨September 2020⁩.

The pseudoElement property of a KeyframeEffect interface is a string representing the pseudo-element being animated. It may be null for animations that do not target a pseudo-element. It performs as both a getter and a setter, except with animations and transitions generated by CSS.

Note: If set to the legacy single-colon syntax of :before, :after, :first-letter, or :first-line, the string is transformed into its double-colon modern version (::before, ::after, ::first-letter, and ::first-line, respectively).

Value

A string or null.

Exceptions

SyntaxError DOMException: Thrown when trying to set this property to an element, an invalid pseudo-element (either non-existent or misspelled). The property is then left unchanged.

Examples

html

<div id="text">Some text</div>
<pre id="log"></pre>

css

#text::after {
  content: "👹";
  display: inline-block; /* Needed as the `transform` property does not apply to inline elements */
  font-size: 2rem;
}
#text::before {
  content: "🤠";
  display: inline-block;
  font-size: 2rem;
}

const log = document.getElementById("log");
const text = document.getElementById("text");

// Create the keyframe and launch the animation
const animation = text.animate([{ transform: "rotate(360deg)" }], {
  duration: 3000,
  iterations: Infinity,
  pseudoElement: "::after",
});

// Get the value of KeyframeEffect.pseudoElement
function logPseudoElement() {
  const keyframeEffect = animation.effect;
  log.textContent = `Value of pseudoElement animated: ${keyframeEffect.pseudoElement}`;
  requestAnimationFrame(logPseudoElement);
}

// Every 6 seconds, switch the pseudo-element animated
function switchPseudoElement() {
  const keyframeEffect = animation.effect;
  keyframeEffect.pseudoElement =
    keyframeEffect.pseudoElement === "::after" ? "::before" : "::after";
  setTimeout(switchPseudoElement, 6000);
}

switchPseudoElement();
logPseudoElement();