invalid selector 🟨 JavaScript

DOMException: Failed to execute 'querySelector' on 'Document': 'x' is not a valid selector

The CSS selector string is invalid — often an ID starting with a digit or containing special characters.

Seen on: JavaScript

Meaning

CSS identifiers can’t start with a digit and characters like : . [ need escaping. IDs generated from data often break selectors.

Common causes

  • ID starting with a number (#1abc)
  • Special characters in IDs/classes
  • Building selectors from user data

⚡ Quick fix

  1. Use getElementById for IDs
  2. Escape with CSS.escape(id)
  3. Use attribute selectors: [id="1abc"]

Detailed fix by platform

JavaScript

  1. document.querySelector('#' + CSS.escape(id))

How to diagnose

  1. Selector — What string was passed?
  2. Recent change — Did it start after a deploy, upgrade, or configuration change? Compare with the last working version.

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