Object.isExtensible() — Description
Objects are extensible by default: they can have new properties added to them, and their [[Prototype]] can be re-assigned.
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Objects are extensible by default: they can have new properties added to them, and their [[Prototype]] can be re-assigned. An object can be marked as non-extensible using one of {{jsxref("Object.preventExtensions()")}}, {{jsxref("Object.seal()")}}, {{jsxref("Object.freeze()")}}, or {{jsxref("Reflect.preventExtensions()")}}.
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MDN Web Docs — files/en-us/web/javascript/reference/global_objects/object/isextensible/index.md :: Description ↗Revision d14bee540b53 · CC-BY-SA-2.5