this2.js

var val = "window.val"

var obj = {
    val: "obj.val",
    innerMethod: function () {
        var val = "obj.val.inner",
            func = function () {
                var self = this;
                return self.val;
            };
        return func;
    },
    outerMethod: function () {
        return this.val;
    }
};

 //This actually gets executed inside window object
console.log(obj.innerMethod()()); //returns window.val

 //Breakdown in to 2 lines explains this in detail
var _inn = obj.innerMethod();
console.log(_inn()); //returns window.val

console.log(obj.outerMethod()); //returns obj.val