JavaScript 继承

20151028 继承

继承（方法）

一、对象冒充

原理：让父类的构造函数成为子类的方法，通过this关键字给所有属性和方法赋值。

function Person(name,age) {
    this.name = name;
    this.age = age;
    this.sayName = function() {
        console.log(this.name);
    }
}
function Student(name,age) {
    this.obj = Person;
    this.obj(name,age);
    delete this.obj;
}
var s1 = new Student("zhangsan","32")


console.log(s1.name); //输出： zhangsan
console.log(s1.age); //输出： 32
s1.sayName(); //输出： zhangsan

二、call和apply的方法

每个对象都有call的方法。——原理还是同象冒充方式一样。

    function Person(name,age) {
        this.name = name;
        this.age = age;
        this.sayName = function() {
            console.log(this.name);
        }
    }

    function Student(name,age,sex) {
        //Person.apply(this,[name,age]);
        Person.call(this,name,age); 【注意传参方式】
        this.sex = sex;
    }
    var stal = new Student("zhangsan", 23, "nan");
    console.log(stal.name);
    console.log(stal.age);
    console.log(stal.sex);
    stal.sayName();

    //call和apply两种方式：
    Person.call(this,name,age);
    Person.apply(this,[name,age]);【注意传参方式】

三、原型链的继承方式

原理:使子类原型对象指向父类的实例以实现继承,即重写类的原型.

原型链的方式不能实现传参.

//父类
function Person(name,age) {
    this.name = name;
    this.age = age;
    this.sayName = function() {
        console.log(this.name);
    };
}

//子类
function Student(name,age) {
    this.constructor(name,age); //通过父类的构造器对属性进行初始化
    this.sex = "male";
}
Student.prototype = new Person; //子类通过原型的方式获得父类对象中的属性
var a = new Student("zhang",23);
console.log(a.name);

代码片段:

Object.prototype.name = "zhangsan";
Object.prototype.sayName = function() {
        console.log(this.name);
    }

function groundfather() {
}
groundfather.prototype = new Object();
console.log(groundfather.prototype); //输出: Object {name: "zhangsan", sayName: function}

function father() {
}
father.prototype = new groundfather();
console.log(father.prototype);      //输出:groundfather {name: "zhangsan", sayName: function}

function son() {
}
son.prototype = new father();
console.log(son.prototype);         //输出:father {name: "zhangsan", sayName: function}


var f1 = new son();
console.log(f1.name); //输出: zhangsan
console.log(f1.sayName);
//输出: function () {
                console.log(this.name);
            }
[依次往上找]

四、混合继承模式的继承方式 ——提高内存使用率

原理: 混合call和原型链

function Person(name, age) {
    this.name = name;
    this.age = age;
}

Person.prototype.sayName = function () {
    console.log(this.name);
};

function Student(name, age, sex) {
    Person.call(this, name, age);
    this.sex = sex;
}
Student.prototype = new Person();

var stu = new Student("zhangsan", 21, "男");
console.log(stu.name, stu.age, stu.sex);
stu.sayName();