继承

原型链直接继承

         function Person() {}
        Person.prototype.foot = 2; 
        Person.prototype.head = 1;
        Person.prototype.name = "老哥";

        function Student(name, no) {
            this.name = name;
            this.no = no;
        }

        function extend (Child ,Parent){//封装
            var  O = function() {} ;  //中间变量
            O.prototype = Parent.prototype ;//继承来自parent的所有东西
            Child.prototype = new  O();//new出来的新对象的所有方法给child
            Child.prototype.constructor = Child ;//把child手动指回来
        }
        extend(Student,Person) ;
        var stu = new Student("老杨", "22");
        alert(stu.name);
        alert(stu.head);

原型链直接继承prototype

       function Person() {}
        Person.prototype.foot = 2; //this 指代Person
        Person.prototype.head = 1;
        Person.prototype.name = "老哥";

        function Student(name, no) {
            this.name = name;
            this.no = no;
        }
        Student.prototype = Person.prototype;
        Student.prototype.constructor = Student;
        var stu = new Student("老杨", "22");
        alert(stu.name);
        alert(stu.head);

原型链继承_prototype属性

function Person() {
            this.foot = 2; //this 指代Person
            this.head = 1;
            this.name = "老哥";
        }

        function Student(name, no) {
            this.name = name;
            this.no = no;
        }

        Student.prototype = new Person();
        //student 也具有了food和head (赋值)
        //添加了新的内容  但是指向未变  未告诉原型
        // var a = 4 ;
        // a = a+1;
        Student.prototype.constructor = Student;
        //告诉原型我加了新的属性

        var stu = new Student("老杨", "22");

        alert(stu.constructor);
        alert(stu.name);
        //若有冲突，加载原函数的的属性

继承_构造函数绑定

 function Person(){
            this.foot = 2 ;
            this.head = 1 ;
            this.favorColor = ["red" , "yellow"] ;
        } 

        function Student(name,no) {
            // Person.call(this) ;
            Person.apply(this) ;
            this.name = name ;
            this.no = no ;
        }

        var stu = new Student ("大师" , "11") ;
        stu.favorColor.push("greed") ;  
        alert(stu.favorColor) ;  //red,yellow,greed

        var stu1 = new Student("老杨" ,"22") ;
        alert(stu1.favorColor) ;  //red,yellow