Question

i got a question when create a javascript object,
when one function invoking another function within the object, do we need to use ‘this’

MyObject = function() {

    this.function_one = function(param) {  
        return param + param;
    };

    this.function_two = function(param) {
        return this.function_one(param) * this.function_one(param);
        // when invoking function_one, do i need to use 'this' ????
    };

}

Answer 1

In this situation, yes. This is because you assign the anonymous function to be a property of the newly constructed object, which is the only way to access it.

It is possible to make it so that this is not required in this.function_two:

// Inside the MyObject constructor:
    function function_one(param) {  
        return param + param;
    }
    // Optional, if you don't care about being able to call
    // function_one from outside the closure
    this.function_one = function_one;

This makes it so that function_one is available as a variable inside the closure created by calling the constructor; making functions available to call two different ways (via free variable and object property) isn’t a very common idiom, though.

I suggest you read this article by Crockford for a better understanding of the different ways you can attach methods to objects.