如何实现继承？

方法一：使用class

class Person{
  constructor(name, age){
    this.name = name
    this.age = age
  }
  sayHi(){
    console.log(`hi, my name is ${this.name}, I'm ${this.age} year's old.`)
  }
}
class Student extends Person {
  constructor(name, age, school, grade) {
    super(name, age)
    this.school = school
    this.grade = grade
  }
  study(){
    console.log("好好学习，天天向上")
  }
}
const lilei = new Student('李雷', 12, '实验小学', 5)
lilei.sayHi()
lilei.study()

方法二: 使用原型链

function Person(name, age){
  this.name = name
  this.age = age
}
Person.prototype.sayHi = function(){
  console.log(`hi, my name is ${this.name}, I'm ${this.age} year's old.`)
}
function Student(name, age, school, grade){
  this.school = school
  this.grade = grade
  Person.call(this, name, age)  
}
Student.prototype.__proto__ = Person.prototype
Student.prototype.study = function(){
  console.log("好好学习，天天向上")
}
const lilei = new Student('李雷', 12, '实验小学', 5)
lilei.sayHi()
lilei.study()

如果禁止使用Student.prototype.__proto__ = Person.prototype，则应使用下面的代码代替

const f = function(){}
f.prototype = Person.prototype
Student.prototype = new f()