Why do I lose the context of this in Javascript?

Question

I have this simple code :

var o = {
    a: 1,
    b: 2,
    f1: function ()
    {
        alert(this.b);
    }
}

var o2 = {
    a: 11,
    b: 22,
    f2: f         


        

Answer 1

If you do it like as follows,

function will be called in o2 context

var o2 = {
    a: 11,
    b: 22,
    f2: function (j){
      this.temp = j;
      this.temp();
    }
};

also these will work too:

f2: function (j){
      j.apply(this);
}

f2: function (j){
      j.apply(o2);
}

Otherwise you call it just like an ordinary function out of context.

j Is ripped out of its context and you did no tricky closures on it(which is not your intent) so for making "this" work in it you need a scope. The this scope in your question for j is window, which has no "b" in it therefore you get an "undefined".