Function.prototype.memoize.js

// A memoize function to store function results of heavy functions
// http://jsfiddle.net/arian/UQsEA/1/


(function(slice){

Function.prototype.memoize = function(hashFn, bind){
    var cache = {}, self = bind ? this.bind(bind) : this, hashFn = hashFn || JSON.stringify;
    return function(){
        return ((key = hashFn(slice.call(arguments))) in cache) 
            ? cache[key] 
            : (cache[key] = self.apply(bind, arguments));
    };
};

})(Array.prototype.slice);


var dotProduct = function(first, second){
    var l = first.length, result = 0;
    if (second.length != l) return;
    while (l--) result += first[l] * second[l];
    console.log('[' + first + '] · [' + second + '] = ' + result);
    return result;
}

var dotProductFast = dotProduct.memoize();

// Calculate the this simple dot products
// since they will not change over time, we can use the memoized function
console.log('first result: '  + dotProductFast([1, 2, 3, 4], [2, 3, 4, 5]));
console.log('second result: ' + dotProductFast([1, 2, 3, 4], [2, 3, 4, 5]));
console.log('third result: '  + dotProductFast([9, 2, 3, 4], [2, 3, 4, 5]));