Mutual recursion is lots of fun.... not.

mutual.recursion.js

// Way #1

function a (num) {
  console.log('a', num);
  num = num + 1;
  if (num > 1000)
  { return num; }
  else {
    setTimeout(function () { b(num); }, 1000);
  }
}

function b (num) {
  console.log('b', num);
  num = num * 2;
  setTimeout(function () { a(num); }, 1000);
}

setTimeout(a(1), 1000);

// Way #2: A better way.

// using async.whilst && _.compose
// in progress