gistfile1.txt

Function.prototype.cached = function(){
	
	// grab the calling function
	var originalFunction = this; 
	
	// add a cache attribute
	originalFunction["cache"] = {}; 
	
	return function() {
		
		// no real smarts here, just grab the first arg for now
		var arg = arguments[0];
		
		// if there is no cached result for the parameter, calculate
		// the value using the appropriate function and cache the result.
		// logging statements + extra code left here so we can verify what's happening for 
		// the purposes of the exercise!
		if (typeof originalFunction.cache[arg] === "undefined") {
			console.log("About to cache the result of " + arg + " being passed to " 
				+ originalFunction.name); 
			originalFunction.cache[arg] = originalFunction(arg);
		} else {
			console.log("Retrieving the cached result of " + arg + " being passed to " 
				+ originalFunction.name); 
		}
		
		// return the cached value (either pre-existing or just set from above)
		return originalFunction.cache[arg];
		
	};
	 
}

// stripped down isPrime function
function isPrime(num) { 
  // everything but 1 can be prime
  var prime = num != 1;
  for ( var i = 2; i < num; i++ ) { 
    if ( num % i == 0 ) { 
      prime = false; 
      break; 
    } 
  } 
  return prime; 
} 

// some Math.sin examples
var cachedSin = Math.sin.cached();
console.log(cachedSin(1));
console.log(cachedSin(2));
console.log(cachedSin(1));
console.log(cachedSin(2));

// some isPrime examples
var cachedIsPrime = isPrime.cached();
console.log(cachedIsPrime(1));
console.log(cachedIsPrime(3));
console.log(cachedIsPrime(1));
console.log(cachedIsPrime(3));