CODEWITHSUNDEEP
javascriptfunctionobjectconstructorprototype
Jakub Mazurkiewicz
Jakub Mazurkiewicz

Reputation: 67

Javascript - Constructor's properties & Prototype

I'm trying to understand one thing about constructors. Namely I don't understand how function object's properties, aka constructor's properties can't be accessed using Foo.prototype.property, example:

//let's create new function object with predefined properties
function Foo() {
    this.name = "Mike"; 
    this.returnName = function() {
                       return 'This persons name is ' + this.name + '.';
                      };
};

//now let's create new object using constructor and prototypal inheritance
var mike = new Foo();

mike.returnName(); //returns "This persons name is Mike."

I understand that mike inherits properties from Foo's prototype. So these properties must be present inside of the prototype. new object points toward the prototype with internal prototype link using __ proto __. I get that. Thing that I can't get around is how this doesn't work:

Foo.prototype.returnName();

Constructor has .prototype link with prototype property and vice versa prototype has .constructor link with the Foo.

I know that calling the Foo(); function first then calling for window.returnName(); would return the sentence, since this context is set to window.

Is this because when I call the method using prototype it assigns it to the window? Is there any way I could access/call this constructor's property?

Upvotes: 1

Views: 48

Answers (2)

Bas Slagter
Bas Slagter

Reputation: 9929

You are not specifying returnName on the prototype of Foo. If you would do it like this:

function Foo(){
    this.name = "Mike"; 
}

Foo.prototype.returnName = function(){
   return 'This persons name is ' + this.name + '.';
};

var mike = new Foo();

mike.returnName();

Things would be different.

Upvotes: 1

Halcyon
Halcyon

Reputation: 57729

The function returnName is not assigned to the prototype of Foo. Instead it's assigned to every instance of Foo, just like the name is "Mike".

Whenever you call new Foo() a new context is created, this is the this context of that instance.

If you call Foo() directly (without new) this is the global object (window).

Upvotes: 0

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