面向对象练习题（原型重构的一些知识）

1、题目

function Fn() {
    this.x = 100;
    this.y = 200;
    this.getX = function () {
        console.log(this.x);
    }
}
Fn.prototype.getX = function () {
    console.log(this.x);
};
Fn.prototype.getY = function () {
    console.log(this.y);
};
let f1 = new Fn;
let f2 = new Fn;
console.log(f1.getX === f2.getX);
console.log(f1.getY === f2.getY);
console.log(f1.__proto__.getY === Fn.prototype.getY);
console.log(f1.__proto__.getX === f2.getX);
console.log(f1.getX === Fn.prototype.getX);
console.log(f1.constructor);
console.log(Fn.prototype.__proto__.constructor);
f1.getX();
f1.__proto__.getX();
f2.getY();
Fn.prototype.getY();

2、仔细看看图片上的内容

function fun(){
    this.a=0;
    this.b=function(){
        alert(this.a);
    }
}
fun.prototype={
    b:function(){
        this.a=20;
        alert(this.a);
    },
    c:function(){
        this.a=30;
        alert(this.a)
    }
}
var my_fun=new fun();
my_fun.b();
my_fun.c();

3、Object.assign

 let obj1 = {
    n: 10,
    m: 20,
    header: {
        a: 100
    }
};
let obj2 = {
    x: 10,
    m: 30,
    header: {
        b: 200
    }
}; 

/* // obj2覆盖obj1
// 只实现浅比较（浅合并）：只对第一级合并
let obj = Object.assign(obj1, obj2);

 console.log(obj === obj1); //true 返回的不是新对象，而是原始的obj1对象
 console.log(obj === obj2); //false 
 
 /* let obj = Object.assign({}, obj1, obj2);
    console.log(obj); //->返回的是第一个参数「也就是全新的一个对象」 */
    

4、题

   function Fn() {
    this.x = 100;
    this.y = 200;
    this.getX = function () {
        console.log(this.x);
    }
}
Fn.prototype = {
    y: 400,
    getX: function () {
        console.log(this.x);
    },
    getY: function () {
        console.log(this.y);
    },
    sum: function () {
        console.log(this.x + this.y);
    }
};
var f1 = new Fn();
var f2 = new Fn;
console.log(f1.getX === f2.getX);
console.log(f1.getY === f2.getY);
console.log(f1.__proto__.getY === Fn.prototype.getY);
console.log(f1.__proto__.getX === f2.getX);
console.log(f1.getX === Fn.prototype.getX);
console.log(f1.constructor);
console.log(Fn.prototype.__proto__.constructor);
f1.getX();
f1.__proto__.getX();
f2.getY();
Fn.prototype.getY();
f1.sum();
Fn.prototype.sum();

注意上面console.log(f1.constructor);输出的是Object函数，因为重写了Fn的原型，所以找不到constructor属性了，就会沿着原型链向上查找

5、new 执行返回的是object

function Foo() {
    getName = function () {console.log(1);};
    return this;
}
Foo.getName = function () {console.log(2);}; 
Foo.prototype.getName = function () {console.log(3);};
var getName = function () {console.log(4);};
function getName() {console.log(5);}

Foo.getName();
getName();
Foo().getName(); 
getName();
var a = new Foo.getName(); // 
var b = new Foo().getName();
var c = new new Foo().getName();
console.log(a,b,c);

6、

function Person() {
    this.name = 'zhufeng'
};
Person.prototype.getName = function () {
    console.log(this.name)
    console.log(this.age)
};
Person.prototype.age = 5000;

var per1 = new Person;
per1.getName();
per1.age = 9;
per1.getName();
console.log(per1.age);
var per2 = new Person;
console.log(per2.age);