How to have function recall private variable between invocations

Question

Here's an easy one straight from the text book I can't seem to find.

I have a javascript function. I want it to contain a private variable which remembers its value between invocations.

Can someone jog my memory please.

Answer 1

Create it using a closure:

function f() {
  var x = 0;
  return function() {return x++;};
}

Then use it as follows:

> g = f()
function () {return x++}
> g()
0
> g()
1
> g()
2