TypeError: Cannot delete property 'x' of #<Object> (V8-based)TypeError: property "x" is non-configurable and can't be deleted (Firefox)TypeError: Unable to delete property. (Safari)

TypeError in strict mode only.

It was attempted to delete a property, but that property isnon-configurable. Theconfigurable attribute controls whether the property can be deleted fromthe object and whether its attributes (other thanwritable) can be changed.

This error happens only instrict mode code. Innon-strict code, the operation returnsfalse.

Non-configurable properties are not super common, but they can be created usingObject.defineProperty() orObject.freeze().

"use strict";const obj = Object.freeze({ name: "Elsa", score: 157 });delete obj.score; // TypeError

"use strict";const obj = {};Object.defineProperty(obj, "foo", { value: 2, configurable: false });delete obj.foo; // TypeError

"use strict";const frozenArray = Object.freeze([0, 1, 2]);frozenArray.pop(); // TypeError

There are also a few non-configurable properties built into JavaScript. Maybe you triedto delete a mathematical constant.

"use strict";delete Math.PI; // TypeError

• delete
• Object.defineProperty()
• Object.freeze()