I read up on JavaScript Iterators and Generators today.
https://developer.mozilla.org/en/JavaScript/Guide/Iterators_and_Generators
https://github.com/davidflanagan/javascript6_examples/blob/master/examples/11.01.linesgenerator.js
http://wiki.ecmascript.org/doku.php?id=harmony:generators
Here's How they wrote the Fibonacci sequence
function fibonacci(){