Homework Exercise 7 part 2

exercise7p2.js

// Part 2.
// Use this new function to refactor the code example.
// Some good test numbers: 524287, 9369319, 2147483647 (all primes)
//
// In other words, if you have this code:
//
//  Function.prototype.cached = function(){
//    ? (what goes here?)
//  }
//  
//  // For the isPrime function
//  
//  var cachedIsPrime = isPrime.cached();
//  isPrime(11); // --> true (cache miss, calls original isPrime(1) function, stores return value in cache)
//  isPrime(11); // --> true (cache hit, directly returns value)
//  
//  // ..but it short work on anything that takes just one (numeric) argument:
//  
//  var cachedSin = Math.sin.cached();
//  
//  cachedSin(1); // --> 0.8414709848078965 (cache miss, calls original Math.sin(1) function, stores return value in cache)
//  cachedSin(1); // --> 0.8414709848078965 (cache hit, directly returns value)

Function.prototype.cached = function() {
  var cache = {}, extendedFunction = this;

  // Non logging version
  //return function(val) {
  //  return cache[val] = (val in cache) ? cache[val] : extendedFunction(val);
  //};

  return function(val) {
    if (val in cache) {
      console.log('cache hit');
    } else {
      console.log('cache miss');
      cache[val] = extendedFunction(val);
    }

    return cache[val];
  }
}

function isPrime(num) { 
  var prime = num != 1;

  for (var i = 2; i < num; i++) { 
    if (num % i == 0) { 
      prime = false; 
      break; 
    } 
  } 
  
  return prime; 
} 

var isPrimeCached = isPrime.cached();

console.log(isPrimeCached(524287));
console.log(isPrimeCached(9369319));
console.log(isPrimeCached(524287));
console.log(isPrimeCached(9369319));