already declared 🟨 JavaScript

SyntaxError: Identifier 'x' has already been declared

The same let/const/class name was declared twice in the same scope.

Seen on: JavaScript

Meaning

Often caused by including the same script twice, redeclaring in the browser console, or two scripts sharing global scope.

Common causes

  • Script loaded twice
  • Duplicate declaration in one scope
  • Re-running code in the console

⚡ Quick fix

  1. Rename or remove the duplicate
  2. Load each script once
  3. Wrap scripts in modules or IIFEs

Detailed fix by platform

JavaScript

  1. Use type="module" scripts so each file has its own scope

How to diagnose

  1. Name — Which identifier?
  2. Load — Is the script included twice?

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