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JS
JavaScript error

TypeError

The JavaScript exception "can't define property "x": "obj" is not extensible" occurs when an object is marked as non-extensible, so that it will never have properties beyond the ones it had at the time it was marked as non-extensible. Objects can be made non-extensible by calling Object.preventExtensions(), Object.seal(), or Object.freeze().

Reference entryJavaScriptFetched
This is a reference entry from MDN Web Docs. A full explanation with fixes has not been written yet.

The error messages

TypeError: Cannot add property x, object is not extensible (V8-based)
As listed by MDN Web Docs
TypeError: Cannot define property x, object is not extensible (V8-based)
As listed by MDN Web Docs
TypeError: can't define property "x": Object is not extensible (Firefox)
As listed by MDN Web Docs
TypeError: Attempting to define property on object that is not extensible. (Safari)
As listed by MDN Web Docs

Details

Category
TypeError
Severity
error
Runtime
both

Related errors

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Source: MDN Web Docs. Data fetched 2026-09-25T01:48:37.273Z.