#### A function within a function?

For a quick review, you may want to glance at JavaScript Kit's tutorial
on Creating Custom
Objects Via JavaScript. This page and the next build heavily on the
concepts introduced there.

It's not a very well-known fact that you can create a function within a
function. You might think that would be a dumb idea -- why not just
define the function normally, outside all functions, like this:

function outerF(x) { return 3 * innerF(x) } function innerF(x) { return 4 * x }

This is certainly a legitimate action. But we are allowed to define inner functions, like this:

function outerF(x) { function innerF(x) { return 4 * x } return 3 * innerF(x) }

What makes this interesting is that the innerF() function is **NOT**
defined outside the outerF() function:

function outerF(x) { function innerF(x) { return 4 * x } alert(innerF(4)) // alerts 16 return 3 * innerF(x) } alert(outerF(5)) // alerts 60 alert(innerF(4)) // throws an exception

You can see this in action (the error is not canceled) by clicking on this sample link.

Right now, you might be thinking, *Okay, so I can have one function
inside another function, and there won't be a reference outside the
function. How do I use that inner function out in the real world?*
JavaScript Kit's objects tutorial gives us the clue, but I'll finish it off
in the next page.

- Choosing unique object names
- A function within a function?
- Exposing inner functions to the outer world