一，类的属性在 constructor 定义和赋值

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

let p = new Person('Jack',21);
console.log('name : ' + p.name + ' , age : ' + p.age);

二，类的 constructor 默认返回类的实例，也可以返回其他类的实例

class Work{
	constructor(company, location){
		this.company = company
		this.location = location
	}
	
	toJson(){
		return {'company' : this.company,'location' : this.location}
	}
}

class Person{
    constructor(name,age){
        this.name = name
        this.age=age
		return new Work('Tencent','Shenzhen')
    }
}

let p = new Person('Jack',21);
console.log(p.toJson());

三，子类继承父类，必须在 constructor 中先执行 super()，才能绑定父类的 this 到子类

class Person  {
    constructor(name,age){
        this.name = name
        this.age=age
    }
	
	info(){
		return {'name' : this.name,'age' : this.age}
	}
}

class Student extends Person {
	constructor(name, age, school, grade){
		super()
		this.school = school
		this.grade = grade
		this.name = name
		this.age = age
	
	}
}

let s = new Student('Jack',21,'SCNU',5);
console.log(s.info());

四，类的实质是函数，自身就是构造函数，可以通过 prototype 和 Object.assign 来修改类的属性和方法

class Person  {
    constructor(name,age){
        this.name = name
        this.age=age
    }
}

Person.prototype.toJson=function(){
    return {'name':this.name,'age':this.age}
}

Object.assign(Person.prototype,{
    getName:function(){
        return this.name;
    }
})


let o = new Person('Jack',21);
console.log(o.toJson());
console.log(o.getName());