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JS
JavaScript error

TypeError

The JavaScript exception "TypeError: can't set prototype: it would cause a prototype chain cycle" occurs when an object's prototype is set to an object such that the prototype chain becomes circular (a and b both have each other in their prototype chains).

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: Cyclic __proto__ value (V8-based)
As listed by MDN Web Docs
TypeError: can't set prototype: it would cause a prototype chain cycle (Firefox)
As listed by MDN Web Docs
TypeError: cyclic __proto__ value (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.