缓存函数memorize

 1 function mulity(x){
 2             return x*x;
 3         }
 4     function memorize(f){
 5             var cache  = {};
 6             var key = arguments.length + Array.prototype.join.call(arguments,",");//参数长度和参数作为属性
 7             if(key in cache)
 8                 return cache[key];
 9             else
10                 return cache[key] = f.apply(this,arguments);
11         };
12         
13     function Test(){
14             var t = memorize(mulity);
15                 var k =t(6);//第一次是直接算
16                 var k2 =t(6);//第二次是调用缓存
17                 alert(k2);
18         }