原型链

下面定义了People类，Student类依赖与People。A为Student的实例

class People {
  constructor (name) {
    this.name = name
  }
  sayHi () {
    console.log(`${this.name} say hi`);
  }
}
class Student extends People {
  constructor (name, grade) {
    // 运行父类的constructor，并传参数
    super(name)
    this.grade = grade
  }
  sayGrade () {
    console.log(`${this.name} is ${this.grade} grade`);
  }
}
const A = new Student('wangyu', 8)

它们之间的原型链关系为：