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Asked: 2026-05-23T19:01:03+00:00

function MyObject(){} Array.prototype={}; MyObject.prototype={}; var a=new Array(); var b=new MyObject(); alert(a.constructor==Array);//true alert(b.constructor==MyObject);//false

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function MyObject(){}
Array.prototype={};
MyObject.prototype={};
var a=new Array();
var b=new MyObject();
alert(a.constructor==Array);//true
alert(b.constructor==MyObject);//false
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1 Answer

  1. Editorial Team

    Array.prototype is a non-writable property.

    As such, your assignment:

    Array.prototype = {}

    …doesn’t succeed, and so its .constructor property hasn’t changed.

    15.4.3.1 Array.prototype

    The initial value of Array.prototype is the Array prototype object (15.4.4).

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

    …whereas with your custom constructor, you have the ability to assign a different prototype object, so you’ve overwritten the original which had reference to the constructor via .constructor.

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