Question

Possible Duplicate:
Why can I use a function before it's defined in Javascript?

As would be expected, the following code throws an error because Foo is not defined:

window.Foo = Foo;

Also as expected, this throws the same error:

window.Foo = Foo;
Foo = function() {
    ...
};

Curiously, this works just fine:

window.Foo = Foo;
function Foo(){
    ...
};

How is this possible? Isn’t JavaScript interpreted line-by-line?

Answer 1

The script is parsed first, allowing your code to call functions that are defined later on.