Javascript prototype usage performance [duplicate]

Question

I want to learn the advantages of using JavaScript prototype. Object prototype usage is increasing performance. I want to see this by usage of memory.

Case-1

    var Foo1 = function (name) {
        this.name = name;
        getFirstName = function() { return "name1"; };
        getLastName = function() { return "name2"; };
    };
    for (var i = 0; i < 1000; i++) {
        var foo1 = new Foo1();
    }

Case-2

    var Foo2 = function (name) {
        this.name = name;
    };

    Foo2.prototype = {
        getFirstName: function () { return "name1"; },
        getLastName: function () { return "name2"; },
    };

    for (var i = 0; i < 1000; i++) {
        var foo2 = new Foo2();
    }

1. which case is using memory more than another?

2. Can I learn memory usage of cases?

3. What is the difference about memory usage of cases?

Answer 1

If you define a function or an object to belong to the prototype then it's shared by all instances and creating an object with new does not create it's own instance of the function/object. In this sense defining something to belong to the prototype uses less memory. The precise difference would be that case 1 (look at comments below because your definition is not proper) would create 1000 instances of each function. Case 2 (again look at the comments below) would create only 1 instance of each function.

However case 2 is not defining in the prototype. You're essentially redefining the prototype there. The correct usage would be:

function Foo2 (name) {
    this.name = name;
};

Foo2.prototype.getFirstName = function () { return "name1"; };
Foo2.prototype.getLastName = function () { return "name2"; };

Your case 1 is also not correctly defined in terms of what you're trying to achieve because getFirstName and getLastName are not defined through this (the instance).