Question

I am working with prototype methods and here is the scenerio

function Foo () {
    this.x = 5;
    this.y = 2;
    this.z = this.addValues();
}
Foo.prototype = {
    addValues:  function (){
        return this.x + this.y; 
    }
}

Obviously this is just a simple example; in real project, there will be lot of activities in the ‘addValue’ function. Is it fine to use ‘this’ keyword 100s of times or caching this to local variable helps any performance improvements. For example, the below will make any difference?

Foo.prototype = {
    addValues:  function (){
        var self = this;
        return self.x + self.y; 
    }
}

Answer 1

this is the standard way to access x and y. You’ll get no improvements from caching this to a local var—if anything, you’re wasting space by declaring self in the first place.

The only possible risk you’d see is with something like this:

var f = new foo();
var stupid = f.addValues;
stupid(); // whoops - this is suddenly the global object, 
          // and your method is broken.

Having said that, I don’t think you’re responsible for people misusing your function, and I wouldn’t worry about it.

Also, by convention, functions meant to be used as constructors should start with a capital letter. Consider renaming foo to Foo