Y Combinator in JavaScript as shown by Douglas Crockford

y-combinator.js

// playlist:
// http://youtu.be/ya4UHuXNygM?list=PL7664379246A246CB
// minute:
// http://youtu.be/ya4UHuXNygM?t=1h8m42s

function y(le) {
	return (function (f) {
		return f(f);
	}(function (f) {
		return le(function (x) {
			return f(f)(x);
		});
	}));
}

var factorial = y(function (fac) {
	return funcntion (n) {
		return n <= 2 ? n : n * fac(n - 1);
	};
});

var number120 = factorial(5);