Y-Combinator.js

const Y = function(F) {
  return (function (h) {
      return h(h)
  })(function(h) {
    return F(function() {
      return h(h).apply(this, arguments)
    })
  })
}


const fib = Y(function(f) {
  return function(i) {
    if (i === 0 || i === 1) {
      return 1
    }
    return f(i - 1) + f(i - 2)
  }
})

console.log(fib)