TypeError: Assignment to constant variable.
Code reassigned a variable declared with const.
Exact message you may see
Assignment to constant variableinvalid assignment to const
Seen on:
JavaScript
Meaning
const prevents reassignment (mutating an object’s properties is still allowed). Use let if the variable must change.
Common causes
- Reassigning a const in a loop or later code
- Incrementing a const counter
- Reassigning an imported binding
⚡ Quick fix
- Use let for variables that change
- Mutate properties instead of reassigning objects
- Create a new variable for the new value
Detailed fix by platform
JavaScript
- javascript
let total = 0; for (const n of nums) total += n;
How to diagnose
- Declaration — Where is it declared?
- Reassignment — Which line changes it?
🔧 Still not fixed?
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Other ways to find it
Where this error sits
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Last updated 10 Oct 2026