CODEWITHSUNDEEP
javascriptprototype
Lac Viet
Lac Viet

Reputation: 720

Javascript constructor function

When trying executing the two following code blocks separately: The first one:

function Hallo() {

}
var some_obj = {
    name: "Fred",
    age: 23,
}
Hallo.prototype = some_obj;
var obj = new Hallo();
obj.constructor;

And the second one:

 function Hallo() {

    }
    Hallo.prototype.name = 'Khanh';
    Hallo.prototype.age = 23;
    var obj = new Hallo();
    obj.constructor;

I got the result in firebug's console is "Object{}" for the first and "Hallo()" for the second. While the second one is pretty simple to understand but the first one is really odd. Because as I know the constructor of the obj Object in the first one is still the same (that is Hallo() function). However I got Object() function in result. I really cann't understand why. Could you help me with it? Thank you!

Upvotes: 1

Views: 566

Answers (2)

xdazz
xdazz

Reputation: 160973

The reason is:

When you do var obj = new Hallo();, then

console.log(obj.constructor === Hallo.prototype.constructor); // true

In your first example, you assigned Hallo.prototype with a new object, whose constructor is function Object (function Object(){...}).

In your second example, the Hallo.prototype.constructor is still function Hallo() {...}

Upvotes: 2

SelaYou
SelaYou

Reputation: 21

prototype will get a reference that point to the constructor by default, int the first function you overwrite the prototype to some_obj, the constructor reference changes at the same time to some_obj's constructor reference --Object's constructor Object()

Upvotes: 1

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