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JS
JavaScript error

TypeError

The JavaScript strict mode-only exception "is read-only" occurs when a global variable or object property that was assigned to is a read-only property.

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 assign to read only property 'x' of #<Object> (V8-based)
As listed by MDN Web Docs
TypeError: "x" is read-only (Firefox)
As listed by MDN Web Docs
TypeError: Attempted to assign to readonly property. (Safari)
As listed by MDN Web Docs

Details

Category
TypeError in strict mode only
Severity
error
Runtime
both

Related errors

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Source: MDN Web Docs. Data fetched 2026-09-25T01:48:37.274Z.