04面向对象编程-01-创建对象 和 原型理解（prototype、__proto__）

var Student = {
    name: ‘Robot‘,
    height: 1.2,
    run: function () {
        console.log(this.name + ‘ is running...‘);
    }
};
var xiaoming = {
    name: ‘小明‘
};
xiaoming.__proto__ = Student; //xiaoming的原型指向了对象Student

// 原型对象:
var Student = {
    name: ‘Robot‘,
    height: 1.2,
    run: function () {
        console.log(this.name + ‘ is running...‘);
    }
};
function createStudent(name) {
    // 基于Student原型创建一个新对象:
    var s = Object.create(Student);
    // 初始化新对象:
    s.name = name;
    return s;
}
var xiaoming = createStudent(‘小明‘);
xiaoming.run(); // 小明 is running...
xiaoming.__proto__ === Student; // true

function Student(name) {
    this.name = name;
    this.hello = function () {
        alert(‘Hello, ‘ + this.name + ‘!‘);
    }
}
//这确实是一个普通函数，如果不写new的话；
//如果写了new，它就是一个构造函数，默认返回this，不需要在最后写return this;
var xiaoming = new Student(‘小明‘);
xiaoming.name; // ‘小明‘
xiaoming.hello(); // Hello, 小明!

//这里的xiaoming原型就指向这个构造函数Student了

xiaoming.constructor === Student.prototype.constructor; // true
Student.prototype.constructor === Student; // true
Object.getPrototypeOf(xiaoming) === Student.prototype; // true
xiaoming instanceof Student; // true

• 前者指向构造函数Student()，相当于是标记自己是和Student这个构造函数发生联系的；
  
• 后者指向是这个原型对象的原型对象，这里是Object
  

• prototype指向的原型对象，也就是xiaoming的老爹，是个没什么多余属性的几乎空白的一个对象，所以xiaoming没得到什么新能力
• 构造函数的原型对象（就是它爹）是一个空的函数 function( ) { } 
  

var laoWang = {
    name: ‘隔壁老王‘,
    height: 1.2,
    run: function () {
        console.log(this.name + ‘ is running...‘);
    }
};

var xiaoming = {
    name: ‘小明‘
};

xiaoming.__proto__ = laoWang; //xiaoming的原型指向了对象Student //相当于告诉小明的爹是谁，比如小明的爹变成了老王

xiaoming.run(); // 小明 is running...  //小明没定义run方法也会使用run()了

function Student(name){
  this.name = name;
  this.run = function(){return this.name + "is running..."}
}
var xiaoming = new Student("xiaoming");
var xiaohong = new Student("xiaohong");
xiaoming.run === xiaohong.run;
//false
----------------------------------------------------------------------
function Student(name){
  this.name = name;
}
Student.prototype.run = function(){return this.name + "is running..."}
xiaoming = new Student("xiaoming");
xiaohong = new Student("xiaohong");
xiaoming.run === xiaohong.run;
//true

function Student(props) {
    this.name = props.name || ‘匿名‘; // 默认值为‘匿名‘
    this.grade = props.grade || 1; // 默认值为1
}
Student.prototype.hello = function () {
    alert(‘Hello, ‘ + this.name + ‘!‘);
};
function createStudent(props) {
    return new Student(props || {})
}

var xiaoming = createStudent({
    name: ‘小明‘
});
xiaoming.grade; // 1