自我学习之es6(6)
es6的新特性里增加了类和类的继承，其实这个特性也是向后台语言借鉴过来的，先来看下es5的时候如何构造一个对象
function Human(){
this.eyes=2;
this.hands=2;
}
Human.prototype.singing=function(){
console.log('I can sing');
}
let a = new Human();
console.log(a);
a.singing();再来看，如何用es6来申明一个类：
class Human{
constructor(){
this.eyes=2;
this.hands=2;
}
}
let a = new Human();
console.log(a);es6用class关键字来申明一个类，并用constructor来创建一个类的构造函数，初始化一个对象的属性，其实es6只是用了一种更语义化、更规范的方式去申明一个类，但是其背后的原理还是基于es5的，如果要创建一个方法，也无需再挂载到原型上 直接在对象里创建
class Human{
constructor(){
this.eyes=2;
this.hands=2;
}
singing(){
console.log('I can sing');
}
}
let a = new Human();
console.log(a);
a.singing();class Human{
constructor(){
this.eyes=2;
this.hands=2;
}
singing(){
console.log('I can sing');
}
}
let a = new Human();
console.log(a);
a.singing();
class NormalMan extends Human {
}
let b=new NormalMan();
console.log(b);类可以继承另外一个类，使用extends语法，可以继承到另外一个类的所有属性和方法，除此之外，它也可以改造继承过来的属性和方法或者创建新的属性和方法
class Human{
constructor(){
this.eyes=2;
this.hands=2;
}
singing(){
console.log('I can sing');
}
}
let a = new Human();
console.log(a);
a.singing();
class NormalMan extends Human {
constructor(){
super();
this.eyes=100;
this.hands=200;
this.feet=2;
}
singing(){
console.log('NormalMan can sing');
}
run(){
console.log('NormalMan can run');
}
}
let b=new NormalMan();
console.log(b);
b.singing();
b.run();我们可以在父类的构造函数里传参，在调用的时候传参
class Human{
constructor(eyes=2,hands=2){
this.eyes=eyes;
this.hands=hands;
}
singing(){
console.log('I can sing');
}
}
let a = new Human(3,4);
console.log(a);
a.singing();
class NormalMan extends Human {
constructor(){
super();
this.eyes=100;
this.hands=200;
this.feet=2;
}
singing(){
console.log('NormalMan can sing');
}
run(){
console.log('NormalMan can run');
}
}
let b=new NormalMan();
console.log(b);
b.singing();
b.run();class Human{
constructor(eyes=2,hands=2){
this.eyes=eyes;
this.hands=hands;
}
singing(){
console.log('I can sing');
}
}
let a = new Human(3,4);
console.log(a);
a.singing();
class NormalMan extends Human {
constructor(){
super(1000,2000);
this.feet=2;
}
singing(){
console.log('NormalMan can sing');
}
run(){
console.log('NormalMan can run');
}
}
let b=new NormalMan();
console.log(b);
b.singing();
b.run();关于构造函数里的this指向，我们可以在继承的函数的构造函数里面传一个name的参数，并在构造函数里新建一个name的属性，在singing()的方法里可以用模板字符串${this.name}去拼接，最后在实例化的NormalMan()里传入Mike，最后打印出来NormalMan这个对象里有name: "Mike"
如果用另外一个变量去接收b里面singing的方法 ，再调用这个方法，这个时候就和运行一个普通函数一样，这时再去打印this，this就为undefined
class Human{
constructor(eyes=2,hands=2){
this.eyes=eyes;
this.hands=hands;
}
singing(){
console.log('I can sing');
}
}
let a = new Human(3,4);
console.log(a);
a.singing();
class NormalMan extends Human {
constructor(name='Flowke'){
super(1000,2000);
this.feet=2;
this.name=name;
}
singing(){
console.log(this);
/*console.log(`${this.name} can sing`);*/
}
run(){
console.log('NormalMan can run');
}
}
let b=new NormalMan('Mike');
console.log(b);
b.singing();
b.run();
let fnn=b.singing;
fnn();class Human{
constructor(eyes=2,hands=2){
this.eyes=eyes;
this.hands=hands;
}
singing(){
console.log('I can sing');
}
}
let a = new Human(3,4);
console.log(a);
a.singing();
class NormalMan extends Human {
constructor(name='Flowke'){
super(1000,2000);
this.feet=2;
this.name=name;
this.singing=this.singing.bind(this);
}
singing(){
/*console.log(this);*/
console.log(`${this.name} can sing`);
}
run(){
console.log('NormalMan can run');
}
}
let b=new NormalMan('Mike');
console.log(b);
b.singing();
b.run();
let fnn=b.singing;
fnn();