trampoline-factorial.js

function factorial(num) {
  if(num <= 1) return num;
  return num * factorial(--num); 
}

function factorialSmart(num) {
  function factorial(acc, num) {
    if(num <=1) return acc;
    return function() { return factorial(acc * num, --num); }
  }
  function trampoline(func) {
    var result = func;
    while(result && typeof(result) === "function"){
      result = result()
    }
    return result;
  }
  return trampoline(factorial(1, num));
}

factorial(1000000) //Uncaught RangeError: Maximum call stack size exceeded(…)
factorialSmart(1000000) //Infinity

Helpful in understanding trampoline functions. One question. In the while loop while do result &&? In other words, it still works if I do while(typeof(result) === "function").