Question

To add a function to an object, i write it inside of it like this AddX:

function Foo()
{
    this.x = 1;

    this.AddX = function(y)
    {
      this.x += y;
    }

}

But I found out that other way could be to use prototype:

function Foo()
{
    this.x = 1;
}

Foo.prototype.AddX = function(y)
{
    this.x += y;
}

Using:

obj = new Foo;
obj.AddX(5);
alert(obj.x);

Result is same in both cases. Which route is best or is there any difference between the two ? Is there any performance issue also ?

Answer 1

In your first approach, addX is an instance method. Thus each instance of Foo will have their own copy of addX.

While in the second approach, addX is a added onto prototype, and each instance of Foo shares the same prorotype.

Thus the second approach will save more memory. If you have a large number of instances to be created, then you’d better use the second approach.