Classes 继承

class Point {
  constructor(x, y) {
    this.x = x
    this.y = y
  }

  toString() {
    return `(${this.x}, ${this.y})`
  }
}

class ColorPoint extends Point {
  constructor(x, y, color) {
    // super() 调用父类的 constructor
    // 调用 super 之后才能使用 this
    super(x, y)
    this.color = color
  }

  toString() {
    // 使用父类的方法
    return super.toString() + ' in ' + this.color
  }
}

const cp = new ColorPoint(25, 8, 'green')
cp.toString() // '(25, 8) in green'
console.log(cp instanceof ColorPoint) // true
console.log(cp instanceof Point) // true

constructor() {
  super()
}