gistfile1.js

// 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.

var sin = function() { return (arguments.length === 0) ? false : Math.sin(arguments[0]); }

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

  return function( arg ) {
    return cache[ arg ] = arg in cache ? cache[ arg ] : func(arg);
  };

}

/*
// Trace version 

Function.prototype.cached = function(){
  var self = this, cache = {};
	return cache[ arg ] = arg in cache ? cache[ arg ] : func(arg);

	return function(arg){ arg in cache ? :  }

  return function(arg){ 
    if(arg in cache) {
      console.log('Cache hit for '+arg);
      return cache[arg];
    } else {
      console.log('Cache miss for '+arg);
      return cache[arg] = self(arg);
    }
  }
}

*/

var cachedSin = sin.cached();
cachedSin(1); // --> 0.8414709848078965 (cache miss, calls original Math.sin(1) function, stores return value in cache)
cachedSin.memory // --> [] ... :( need direction here
cachedSin(1); // --> 0.8414709848078965 (cache hit, should directly return value based on what's in the memory variable at position 1)