Homework 2

<script>
// Part 1
// Implement a function prototype extension that caches function results for
// the same input arguments of a function with one parameter.

Function.prototype.withCaching = function withCaching() {
  if (!this.cache) { this.cache = {}; }
  var method = this;
  return function(input) {
    if (typeof method.cache[input] == "undefined") {
      var result = method.apply(this, [input]);
      method.cache[input] = result;
    }
    return method.cache[input];
  };
}

// Part 2
// Use this new function to refactor the code example.
// Some good test numbers: 524287, 9369319, 2147483647 (all primes)

var isPrime = function(num) {
  console.log("looking ...");
  var prime = num != 1;
  // everything but 1 can be prime
  for (var i = 2; i < num; i++) {
    if (num % 1 == 0) {
      prime = false;
      break;
    }
  }
  return prime;
}.withCaching();

console.log(isPrime(4));
console.log(isPrime(4));

console.log(isPrime(524287));
console.log(isPrime(524287));

</script>