gistfile1.js

// Para rectificar con http://gist.github.com/500794

  // Part 1.
  // Implement a function prototype extension that caches function results for
  // the same input arguments of a function with one parameter.
  //
  // For example:
  // Make sin(1) have the result of Math.sin(1), but use a cached value
  // for future calls.
  //
  
  Object.extend = function(destination, source) { 
    for (var property in source) {
      destination[property] = source[property]; 
    }
    return destination;
  };
  
  Object.extend(Function.prototype, {
    cache: function(k, v) {
      if (!this.cache[k]) {
        this.cache[k] = v;
      }
      return this.cache[k];
    }
  });
  
  var sin = function(num) {
    return sin.cache[num] || sin.cache(num, Math.sin(num));
  };
    
  // Part 2.
  // Use this new function to refactor the code example.
  // Some good test numbers: 524287, 9369319, 2147483647 (all primes)
  
  function isPrime(num) { 
    return isPrime.cache[num] || 
           isPrime.cache(num, function(num){
             // everything but 1 can be prime
             var prime = num != 1,
                 i = 2;

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