SOURCE

class Parent {
  constructor (name, age) {
    this.name = name
    this.age = age
    this.showName = function() {
      return this.name
    }
  show = () => {
    return 22
  }
  showAge () {
    return this.age
  }
}
console.log(Parent.prototype)
let p = new Parent('zhangli', '30')
for(let key in Parent.prototype) {
  console.log(key)
}

class Child extends Parent {
  constructor (name, age) {
    super(name, age)
  }
}
let c = new Child('yueyue', 2)
console.log(c.showAge())