gistfile1.txt

// 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.

Function.prototype.cached = function() {
  var fn = this,
      cache = [];
  
  return function() {
    var arg = arguments[0];
    
    if (arg in cache) {
      return cache[arg];
    }
    
    return (cache[arg] = fn(arg));
  };
};

sin = Math.sin.cached();

sin(Math.PI/2);
// => 1

sin(Math.PI/2);
// => 1 (cached)


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

isPrime = function(num) {
  var prime = num != 1;
  for ( var i = 2; i < num; i++ ) { 
    if ( num % i == 0 ) { 
      prime = false; 
      break; 
    } 
  }
  return prime;
}.cached();