Friday afternoon scoping quiz

[Brendan Eich]

On Feb 5, 2010, at 2:14 PM, P T Withington wrote:

> ({
>  'foo': 20,
>  'test': function () {
>    var f = function () {
>      alert("foo:"+ foo);
>      alert("this.foo:"+ this.foo);
>      alert("bar:"+ bar);
>    }
>    with (this) {
>      var foo = 42;
>      var bar = 21;
>      f.call(this);
>    }

"Doctor, it hurts when I use 'with' in JavaScript!"


>  }
> }).test();
>
> --
>
> By my reading, `foo` and `bar` are declared and initialized in  
> `test`, and closed over by `f`.  I expect to see:
>
> foo:42
> this.foo:20
> bar:21
>
> But in Rhino, Firefox, Safari and Opera I am seeing:
>
> foo:undefined
> this.foo:42
> bar:21

This is correct. The vars are hoisted but the initialization of foo  
puts 42 where it found foo on the scope chain, in this.foo. There's no  
'bar' property in |this| so that goes in the var.


> Flash 10 gives me the answer I expected.  I have not tested other JS  
> engines.

Flash 10 bug.

/be