wow Y combinator.js?

factorial.js

// Simple
const simpleRecursive = () => simpleRecursive()
simpleRecursive()

// "simpleRecursive" is undefined! (static check)
const notSoSimpleRecursive = me => me(me)
notSoSimpleRecursive(notSoSimpleRecursive)

// Don't run forever!
const factorial = (me, n) => n < 1 ? 1 : n * me(me, n - 1)
factorial(factorial, 10)

// Save some lines :D
;((me, n) => n < 1 ? 1 : n * me(me, n - 1))((me, n) => n < 1 ? 1 : n * me(me, n - 1), 10)

// Now we may have a Y Combinator from Lambda Calculus
const againFactorial = x => ((me, n) => n < 1 ? 1 : n * me(me, n - 1))((me, n) => n < 1 ? 1 : n * me(me, n - 1), x)