Question

var a = function () {};
a.prototype.test  = function () {
alert("hello");
} 

works fine but in following code

var b = new Object();
b.prototype.test  = function () {
alert("hello");
} 

i am getting this error TypeError: Cannot set property ‘test’ of undefined and i am unable to get it.

As per my understanding b has inherited prototype object from Object. So we should be able to add a new property in following manner say b.prototype.x = 1 .

But Object.prototype.x = 1 works .

typeof Object and a gives function but that of b is object

I am not getting why b.prototype.x = 1 doesnt work

Thanks.

Answer 1

Object is a function, which has a prototype property.

new Object() creates an object, which does not have a prototype property.

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If you want to set the prototype of an object, you might mean setting the prototype of the object’s constructor.

b.constructor.prototype.test = ...

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To clarify some of the prototype/constructor nonsense:

A function has a prototype, which is an object. It specifies properties to add to an instance of that function.

An object has a constructor, which is a function. It specifies the function that was used to create the object.

Note that a function is an object, so it also has a constructor, which is Function.