Y-Combinator

index.js

var Y = require('./y');

function factorial(proc) {
  return function (n) {
    return n === 0 ? 1 : (n * proc(n - 1));
  }
}
var fact = Y(factorial);
var r = fact(3);
console.log(r);

function findMax(proc) {
  return function (array) {
    if (array.length < 1) return 0;
    var element = array[0];
    return Math.max(element, proc(array.splice(1)));
  }
}
var max = Y(findMax);
var r = max([0, 5, -3, -2, -1]);
log(r);

function log(x) {
  console.log(x);
}

y.js

function Y(outer) {
  function inner(proc) {
    function apply(arg) {
      return proc(proc)(arg);
    }

    return outer(apply);
  }

  return inner(inner);
}

module.exports = Y;