A recursive, caching JavaScript implementation of the famous Fibonacci function. Each time you call it, it gets faster.

fastFibonacci.js

var fibonacci=function()
{
	var x=[0,1];
	return function(n)
	{
		if(x[n]!==undefined)
		{
			return x[n];
		}
		else
		{
			x[n]=fibonacci(n-1)+fibonacci(n-2);
			return x[n];
		}
	}
};
fibonacci=fibonacci();

print( fibonacci(7) );