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(xiàn)重載，利用arguments.length的不同來實現(xiàn) 
  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); 
    } 
  }