Question

Consider this:

function f2(x) {
    return x+1;
};

X = function(){
    this.f1=function (x) {
      return 2*f2(x);
    }

    return this;
};

then x = new X(); x.f1(1) works fine.

But when i want to do this:

X = function(){
    this.f2 = function(x) {
        return x+1;
    };

    this.f1=function (x) {
        return 2*f2(x);
    }

    return this;
};

The same statement will complain that it can’t find f2.
In, for example c#, you can say

class X {
   int f2(int x){return x+1;}
   int f1(int x){return 2*f2(x);}
}

and this will work

X x=new X();
x.f1(1)

Why?

Answer 1

To reference f2 in your second code block, you’ll need to use this.f2. this references the context in which the function is being executed. Since you call f1 in the following way:

x.f1();

… the context is set to the instance, x.

JavaScript does not make instance variables available to the scope in the same way as scope variables, i.e. those directly available:

X = function(){

    var f2 = 123;

    this.f2 = function(x) {
        return x+1;
    };

    this.f1=function (x) {

        console.log(f2); // => 123
        console.log(this.f2); // => function(){}

        return 2 * this.f2(x);
    };

    return this;
};