Question

I know that top-level functions are members of the window object, and it’s consistent with the fact that this inside them refers to the window.

But for non-top level functions, this is still window, but they are not members of window!

Here’s some code:

function topLevel1() {
    alert(this)
}

function topLevel2() {
    function inner() {
        alert(this)
    }

    inner()
}

topLevel1()                // alerts DOMWindow
alert(window.topLevel1)    // alerts text of topLevel1, as expected

topLevel2()                   // again, alerts DOMWindow
alert(window.inner)           // undefined
alert(window.topLevel2.inner) // undefined

1. If inner is neither a member of window nor of topLevel2, whose member is it?
2. How can it be that it’s this is window, but it’s not a window‘s member?
3. Isn’t it a law in Javascript that if this == owner, then the current method was called via owner.? (except special cases like constructors, apply, call, etc)

Answer 1

Again, the this value of a function is decided of how the function is invoked, not where it is located or how it was designed.

If you just call a function

foobar()

anywhere in your code, just like that, its this value will always be window (non-strict mode) or undefined (strict). Now there are plenty of ways to modify the this, like calling the function with .apply(), .call() or .bind(). All of those methods give your the opportunity to modify the this value for a given function. Also, if you call a function with the new keyword, this referes to a newly created object (which is also returned).

So, location of a function tells you zero about its context or this.

Now to answer your specific questions:

1. inner is a member of the Activation Object from topLevel2 (ES3)

2. described above

3. I guess thats also covered above