Function类型

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• callee:arguments对象的属性,该属性是一个指针,指向拥有这个arguments对象的函数.

          /*function factorial(num){
              if (num <= 1) {
                  return 1;
              } else {
                  return num * factorial(num-1)
              }
          }*///此方法等价于下面这个方法
  
          function factorial(num){
              if (num <= 1) {
                  return 1;
              } else {
                  return num * arguments.callee(num-1)
              }
          }
  
          var trueFactorial = factorial;
          
          factorial = function(){
              return 0;
          };
          
          alert(trueFactorial(5));   //120
          alert(factorial(5));       //0

   

• 每个函数都有两个方法:apply()和call() 

1. apply():接受两个参数:一个是在其中运行函数的作用域,另一个是参数数组.其中,第二个参数可以是Array实例,也可以是arguments对象.

           function sum(num1, num2){
               return num1 + num2;
           }
           
           function callSum1(num1, num2){
               return sum.apply(this, arguments);
           }
           
           function callSum2(num1, num2){
               return sum.apply(this, [num1, num2]);
           }
           
           alert(callSum1(10,10));   //20
           alert(callSum2(10,10));   //20

    

2. call():第一个参数和apply一样,其余的参数是直接传.

           function sum(num1, num2){
               return num1 + num2;
           }
           
           function callSum(num1, num2){
               return sum.call(this, num1, num2);
           }
           
           alert(callSum(10,10));   //20

    

• apply()和call()的真正用处:

        window.color = "red";
        var o = { color: "blue" };
        
        function sayColor(){
            alert(this.color);
        }
        
        sayColor();            //red
        
        sayColor.call(this);   //red
        sayColor.call(window); //red
        sayColor.call(o);      //blue

• 函数还有一个方法:bind(),可以绑定函数的运行环境

          window.color = "red";
          var o = { color: "blue" };
                             
          function sayColor(){
              alert(this.color);
          }
          var objectSayColor = sayColor.bind(o);
          objectSayColor();   //blue

   

• 函数还有一个length属性:表示函数希望接受的命名参数的个数

          function sayName(name){
              alert(name);
          }      
          
          function sum(num1, num2){
              return num1 + num2;
          }
          
          function sayHi(){
              alert("hi");
          }
          
          alert(sayName.length);  //1
          alert(sum.length);      //2
          alert(sayHi.length);    //0

   

转载于:https://my.oschina.net/langgege/blog/1058111