Modify build-in Object prototype

Question

String.prototype = new Number();
console.log(String.prototype.__proto__ === Number.prototype);//return false

why i cant change the prototype chain of bulid-in Object.

Christian C. Salvadó · Accepted Answer · 2011-10-02 04:39:01Z

3

This is because the prototype property of built-in constructors¹ is non-writable (also non-configurable and non-enumerable).

See the property attributes:

Object.getOwnPropertyDescriptor(String, 'prototype');

/*
configurable: false,
enumerable: false,
writable: false
*/

This is described in each built-in constructor, for the String.prototype property see :

15.5.3.1 String.prototype

...

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

¹: by "built-in constructor" I refer to the constructor functions defined on the global object: String, Number, Boolean, Object, Array, Function, Date, RegExp, Error (and other NativeError types).

answered Oct 2, 2011 at 4:16

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