Since ECMA-/Javascript is all about Objects and Contexts (which, are also somekind of Object), every variable is stored in a such called Variable- (or in case of a Function, Activation Object).
So if you create variables like this:
var a = 1,
b = 2,
c = 3;
In the Global scope (= NO function context), you implicitly write those variables into the Global object (= window in a browser).
Those can get accessed by using the “dot” or “bracket” notation:
var name = window.a;
or
var name = window['a'];
This only works for the global object in this particular instance, because the Variable Object of the Global Object is the window object itself. Within the Context of a function, you don’t have direct access to the Activation Object. For instance:
function foobar() {
this.a = 1;
this.b = 2;
var name = window['a']; // === undefined
alert(name);
name = this['a']; // === 1
alert(name);
}
new foobar();
new creates a new instance of a self-defined object (context). Without new the scope of the function would be also global (=window). This example would alert undefined and 1 respectively. If we would replace this.a = 1; this.b = 2 with:
var a = 1,
b = 2;
Both alert outputs would be undefined. In that scenario, the variables a and b would get stored in the Activation Object from foobar, which we cannot access (of course we could access those directly by calling a and b).