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TypeError: property "x" is non-configurable and can't be deleted - JavaScript | MDN
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TypeError: property "x" is non-configurable and can't be deleted

The JavaScript exception "property is non-configurable and can't be deleted" occurs when it was attempted to delete a property, but that property is non-configurable.

In this article

Message

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)

Error type

TypeError in strict mode only.

What went wrong?

It was attempted to delete a property, but that property is non-configurable. The configurable attribute controls whether the property can be deleted from the object and whether its attributes (other than writable) can be changed.

This error happens only in strict mode code. In non-strict code, the operation returns false.

Examples

Attempting to delete non-configurable properties

Non-configurable properties are not super common, but they can be created using Object.defineProperty() or Object.freeze().

js
"use strict";
const obj = Object.freeze({ name: "Elsa", score: 157 });
delete obj.score; // TypeError
js
"use strict";
const obj = {};
Object.defineProperty(obj, "foo", { value: 2, configurable: false });
delete obj.foo; // TypeError
js
"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 tried to delete a mathematical constant.

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

See also

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    50. SyntaxError: invalid identity escape in regular expression
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    52. SyntaxError: invalid property name in regular expression
    53. SyntaxError: invalid range in character class
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    55. SyntaxError: invalid regular expression flag "x"
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    60. SyntaxError: missing ) after argument list
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    66. SyntaxError: missing formal parameter
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    70. SyntaxError: new keyword cannot be used with an optional chain
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    92. TypeError: 'caller', 'callee', and 'arguments' properties may not be accessed
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    106. TypeError: can't define property "x": "obj" is not extensible
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    125. TypeError: Reduce of empty array with no initial value
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  14. Misc
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