diff -r 000000000000 -r 6474c204b198 js/src/Y.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/Y.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,14 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// The Y combinator, applied to the factorial function
+
+// Return the function that is the fixed point of f.
+var Y = f => (x => f(v => x(x)(v)))
+             (x => f(v => x(x)(v)));
+
+// The factorial function is the fixed point of this:
+var f = fac => n => (n <= 1) ? 1 : n * fac(n - 1);
+
+print("5! is " + Y(f)(5));