04面向对象编程-02-原型继承 和 ES6的class继承

function Student(props) {
    this.name = props.name || ‘Unnamed‘;
}
Student.prototype.hello = function () {
    alert(‘Hello, ‘ + this.name + ‘!‘);
}

function PrimaryStudent(props) {
    // 调用Student构造函数，绑定this变量
    Student.call(this, props);
    this.grade = props.grade || 1;
}

new PrimaryStudent() ----> PrimaryStudent.prototype ----> Object.prototype ----> null

new PrimaryStudent() ----> PrimaryStudent.prototype ----> Student.prototype ----> Object.prototype ----> null

new PrimaryStudent() ----> Student.prototype ----> Object.prototype ----> null

var bridge = {};  //创建一个没有内容的对象
bridge.__proto__ = Student.prototype;  //让这个对象的原型对象是Student.prototype
bridge.constructor = PrimaryStudent;  //让这个对象的构造函数为PrimaryStudent
PrimaryStudent.prototype = bridge;  //让PrimaryStudent的原型对象指向bridge

这样一来，原型链就变成了：
new PrimaryStudent() ----> PrimaryStudent.prototype(bridge) ----> Student.prototype ----> Object.prototype ----> null

按照我们比喻的说法，就是：
- 让Student有个儿子bridge（bridge.__proto__ = Student.prototype;）
- 然后这个娃和PrimaryStudent结婚了（bridge.constructor = PrimaryStudent; PrimaryStudent.prototype = bridge;）
- 那么自然PrimaryStudent的子女（通过PrimaryStudent创建的对象），既会老爹bridge的技能，也会爷爷Student的技能”

//验证一下
bridge.do = function(){alert("hahaha")};
var xiaoming = new PrimaryStudent({name:‘xiaoming‘, grade:2});
xiaoming.do(); // 弹框alert("hahaha");

//验证原型
xiaoming.__proto__ === PrimaryStudent.prototype; //true
xiaoming.__proto__.__proto__ === Student.prototype; //true

//验证继承关系
xiaoming instanceof PrimaryStudent; //true
xiaoming instanceof Student; //true

// PrimaryStudent构造函数:
function PrimaryStudent(props) {
    Student.call(this, props);
    this.grade = props.grade || 1;
}
// 空函数F，用于后面起桥接作用
function F() {
}
// 把F的原型指向Student.prototype，这样通过F创建的对象，其__proto__属性就是Student.prototype
F.prototype = Student.prototype;
// 把PrimaryStudent的原型指向一个新的F对象，F对象的原型正好指向Student.prototype
PrimaryStudent.prototype = new F();
// 把PrimaryStudent原型的构造函数修复为PrimaryStudent
PrimaryStudent.prototype.constructor = PrimaryStudent;
// 继续在PrimaryStudent原型（就是new F()对象）上定义方法
PrimaryStudent.prototype.getGrade = function () {
    return this.grade;
};
// 创建xiaoming
var xiaoming = new PrimaryStudent({
    name: ‘小明‘,
    grade: 2
});
xiaoming.name; // ‘小明‘
xiaoming.grade; // 2
// 验证原型
xiaoming.__proto__ === PrimaryStudent.prototype; // true
xiaoming.__proto__.__proto__ === Student.prototype; // true
// 验证继承关系
xiaoming instanceof PrimaryStudent; // true
xiaoming instanceof Student; // true

function inherits(Child, Parent) {
    var F = function () {};
    F.prototype = Parent.prototype;
    Child.prototype = new F();
    Child.prototype.constructor = Child;
}

function Student(props) {
    this.name = props.name || ‘Unnamed‘;
}
Student.prototype.hello = function () {
    alert(‘Hello, ‘ + this.name + ‘!‘);
}
function PrimaryStudent(props) {
    Student.call(this, props);
    this.grade = props.grade || 1;
}
// 实现原型继承链:
inherits(PrimaryStudent, Student);
// 绑定其他方法到PrimaryStudent原型:
PrimaryStudent.prototype.getGrade = function () {
    return this.grade;
};