原型函數的類型

原型函數創建總結

1.原型函數的理解圖

2.聲明一個函數就會自動創建一個prototype屬性,這個屬性指向這個函數的原型對象,

而這個函數的原型的對象默認有個constructor屬性,指向最初創建的函數

3.原型函數的變形

• 一般形式

  function Person(){
  ​
      }
      Person.prototype.name = "Tom";
      Person.prototype.speak = function(){
          console.log("abc");
      }
      var p1 = new Person();
      console.log(Person.prototype.constructor === Person);  //true
      console.log(p1.__proto__ === Person.prototype); //true
      console.log(p1.hasOwnProperty("name"));
      console.log(p1.hasOwnProperty("age"));
      console.log("sex" in p1);

• 判斷對象的屬性位置

  
  function position(obj,proName){
          if(obj.hasOwnProperty(proName)){
              return "在對象上";
          }else if(proName in obj){
              return "在原型上";
          }else{
              return "不存在";
          }
      }
      console.log(position(p1,"name"));
      console.log(position(p1,"age"));
      console.log(position(p1,"sex"));

• 組合模型,解決原型的方法共用問題

  
  function Person(name,age){
          this.name = name;
          this.age = age;
      }
      Person.prototype.speak = function(){
          console.log(this.name);
      }
      var p1 = new Person("Tom",22);
      var p2 = new Person("Rose",20);
      console.log(p1.speak());

• 動態原型

  
  function Person(name,age){
          this.name = name;
          this.age = age;
          // 避免每次創建一個對象時重新創建這個方法覆蓋之前的方法
          if(!Person.prototype.eat){
              Person.prototype.eat = function(){
                  console.log(this.name);
              }   
          }
  ​
          if(!Person.prototype.speak){
              Person.prototype.speak = function(){
                  console.log(this.age);
              }
          }
      }
      var p1 = new Person("Tom",22);
      var p2 = new Person("Rose",23);
      console.log(p1.eat == p2.eat);

• 更換原型

  
  function Person(opt){
          this._init(opt);
      }
      Person.prototype = {
          _init : function(opt){
              this.name = opt.name;
              this.age = opt.age;
              this.sex = opt.sex;
          },
          eat : function(){
  ​
          },
          speak : function(){
  ​
          }
      }
      var p1 = new Person({
          name : "Tom",
          age : 22,
          sex : "男"
      });
      var p2 = new Person({
          name : "Tim",
          age : 21,
          sex : "女"
      });

  ​