Why can't this be a primitive?

Question

I was messing around with JavaScript, and noticed that this can never be a primitive. What am I talking about? Let me explain.

Take this function for example.

function test(){
    return typeof this;
}
test.call('Abc'); // 'object'
test.call(123); // 'object'

They are both 'object', not 'string' or 'number', like I'd expect.

After a bit of confusion (and messing with instanceof), I figured out what's going on. 'Abc' is being coverted to a String object, and 123 is being converted to a Number object.

Anyway, my question is why does this happen, and how do I convert an object back to its primitive?

I know I could use (String)this or (Number)this, but how can I do that if I don't know the type?

EDIT: I was trying to do this:

function element(){
    var $e = $(this),
    $d = $e.closest('div');
}
element.call('#myID');

and it wasn't working. this is a String object, and jQuery just made a collection of objects instead of using the selector to search the DOM.