JavaScript中使用參數個數實現重載功能

function overload(){ 
 switch(arguments.length){ 
 case 0: 
 console.log("一個朋友都沒有"); 
 break; 
 case 1: 
 console.log("有一個朋友"); 
 break; 
 case 2: 
 console.log("有兩個朋友"); 
 break; 
 case 3: 
 console.log("有三個朋友"); 
 break; 
 case 4: 
 console.log("有四個朋友"); 
 break; 
 //等等 
 } 
 } 

window.onload=function (){ 
 var cat={ 
 friends:["mimi","pp","gg"] 
 } 
 addMethod(cat,"sayName",function(a,b){ 
 console.log("有兩個朋友"); 
 }) 
 addMethod(cat,"sayName",function(){ 
 console.log("一個朋友都沒有"); 
 }) 
 addMethod(cat,"sayName",function(a){ 
 console.log("有一個朋友"); 
 }) 
 addMethod(cat,"sayName",function(a,b,c){ 
 console.log("有三個朋友"); 
 }) 
 cat.sayName("xiaoming","nihao"); 
 cat.sayName(); 
 cat.sayName("xiaoming"); 
 cat.sayName("xiaoming","xiaohong"); 
 } 
 //實現重載，利用arguments.length的不同來實現 
 function addMethod(object,name,fn){ 
 var old=object[name]; 
 object[name]=function(){ 
 if(fn.length==arguments.length) 
 return fn.apply(this,arguments); 
 else if(typeof old=='function') 
 return old.apply(this,arguments); 
 } 
 }