JavaScript Element pseudo() Method

What You’ll Learn

Element.pseudo() is an experimental instance method that returns a CSSPseudoElement for a given pseudo-element type such as ::before or ::after. Learn the MDN basic demo, how type, parent, and element relate, invalid-type null returns, feature detection, and five try-it labs aligned with MDN.

Introduction

CSS pseudo-elements like ::before and ::after decorate elements from stylesheets. For years, JavaScript could only style them indirectly—for example with getComputedStyle()—but not hold a live object representing the pseudo-element itself.

pseudo(type) bridges that gap (MDN). Pass a valid pseudo-element type string and receive a CSSPseudoElement you can inspect: its type, the parent element that directly originated it, and the ultimate element in the tree.

This page is part of JavaScript Element. Compare with matches() for selector testing on real elements, and getAttribute() for reading element attributes.

Understanding the pseudo() Method

Calling el.pseudo(type) asks the browser for the CSSPseudoElement associated with type on el.

• It is an instance method on Element (MDN).
• type must be a valid pseudo-element type string such as "::after".
• Returns a CSSPseudoElement when type is valid (MDN).
• Returns null when type is not a valid pseudo-element type (MDN).
• MDN: a valid type still returns an instance even if the pseudo-element has not been generated on the element yet.
• The returned object exposes type, parent, and element (MDN).
• CSSPseudoElement also has its own pseudo() for nested pseudo-elements (MDN).

📝 Syntax

General form of Element.pseudo (MDN):

pseudo(type)

Parameters

Return value

Common pseudo-element types

• ::before and ::after — generated content boxes.
• ::first-line and ::first-letter — typographic fragments.
• ::marker — list item markers.
• ::placeholder — placeholder text in form controls.
• ::selection — highlighted user selection.

Common patterns

// MDN basic example
const pElem = document.getElementById("someParagraph");
const pseudoElem = pElem.pseudo("::after");
console.log(pseudoElem.type);   // "::after"
console.log(pseudoElem.parent); // the <p> element

// Feature-detect before calling
if (typeof el.pseudo === "function") {
  const before = el.pseudo("::before");
  if (before) console.log(before.element.tagName);
}

// Invalid type returns null
console.log(el.pseudo("::not-a-real-pseudo")); // null

// Safe wrapper for unsupported browsers
function getPseudo(el, type) {
  try {
    return typeof el.pseudo === "function" ? el.pseudo(type) : null;
  } catch {
    return null;
  }
}

Examples Gallery

Examples follow MDN Element.pseudo() patterns. Use View Output or Try It Yourself for each case.

const pElem = document.getElementById("someParagraph");
const pseudoElem = pElem.pseudo("::after");

console.log(pseudoElem.type);   // "::after"
console.log(pseudoElem.parent); // the <p> element (MDN)

type: ::after
parent tag: P

const quote = document.querySelector("q");
const before = quote.pseudo("::before");

console.log(before.type);              // "::before"
console.log(before.element === quote); // true
console.log(before.parent === quote);  // true for ::before (MDN)

type: ::before
element is quote: true
parent is quote: true

const el = document.getElementById("someParagraph");
const supported = typeof el.pseudo === "function";

console.log(supported ? "pseudo() available" : "pseudo() not supported");

if (supported) {
  const after = el.pseudo("::after");
  console.log(after ? after.type : "null");
}

pseudo() available (or not supported message)
::after

const el = document.getElementById("someParagraph");

const valid = el.pseudo("::after");
const invalid = el.pseudo("::not-a-real-pseudo");

console.log(valid !== null);   // true (when supported)
console.log(invalid === null); // true (MDN)

true
true

const box = document.getElementById("plainBox");
// No ::marker CSS on this div

const marker = box.pseudo("::marker");

console.log(marker !== null); // true when type is valid (MDN)
console.log(marker.type);     // "::marker"

true
::marker

🚀 Common Use Cases

• Inspect pseudo-element metadata (type, parent, element) in devtools-style scripts.
• Bridge CSS pseudo-elements and JavaScript object model APIs (MDN).
• Prototype tooling that walks nested pseudo-elements via CSSPseudoElement.pseudo().
• Feature-detect experimental CSSOM support before building UI that depends on it.
• Compare pseudo-element access with getComputedStyle(el, "::before") for styling tasks.
• Educational demos showing how ::before and ::after relate to their host elements.

📝 Notes

• Experimental on MDN — feature-detect before production use.
• Returns CSSPseudoElement for valid types; null for invalid types (MDN).
• Valid type still returns an object even when the pseudo-element is not generated yet (MDN).
• Use double-colon syntax: "::before", "::after".
• parent is the immediate originator; element is the ultimate originating element (MDN).
• Related: matches(), prepend(), shadowRoot, JavaScript hub.

💡 Best Practices