SyntaxError: Identifier 'x' has already been declared
The same let/const/class name was declared twice in the same scope.
Exact message you may see
has already been declaredredeclaration of let
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
- Rename or remove the duplicate
- Load each script once
- Wrap scripts in modules or IIFEs
Detailed fix by platform
JavaScript
- Use
type="module"scripts so each file has its own scope
How to diagnose
- Name — Which identifier?
- Load — Is the script included twice?
🔧 Still not fixed?
Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:
Similar errors
Most viewed in JavaScript
- TypeError TypeError: Cannot read properties of undefined (reading 'x')
- Failed to fetch TypeError: Failed to fetch / NetworkError when attempting to fetch resource
- module MIME type Failed to load module script: Expected a JavaScript module script but the server responded with a MIME type of "text/html"
Other ways to find it
Where this error sits
Origin: On your device. Errors that are often confused with or caused by this one (click to open):
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Last updated 11 Oct 2026