利用es6 new.target来对模拟抽象类的方法

new Symbol()

// error
Uncaught TypeError: Symbol is not a constructor
  at new Symbol (<anonymous>)
  at <anonymous>:1:1

function disConstructor() {
 if (this !== window) {
  throw new TypeError(' disConstructor is not a constructor')
 }
 console.log('gogo go')
}

// 测试结果如下
disConstructor() // gogo go

new disConstructor()

// error
Uncaught TypeError: disConstructor is not a constructor
  at new disConstructor (<anonymous>:3:15)
  at <anonymous>:1:1

function disConstructor() {
 // 普通的函数调用中，new.target 的值是undefined。
 if (new.target) {
  throw new TypeError(' disConstructor is not a constructor')
 }
 console.log('gogo go')
}

class Animal {
 constructor(name, age) {
  if (new.target === Animal) {
   throw new Error('Animal class can`t instantiate');
  }
  this.name = name
  this.age = age
 }
 // 其他代码
 ...
}

class Dog extends Animal{
 constructor(name, age, sex) {
  super(name, age)
  this.sex = sex
 }
}

new Animal()
// error
Uncaught Error: Animal class can`t instantiate
  at new Animal (<anonymous>:4:13)
  at <anonymous>:1:1

new Dog('mimi', 12, '公')
// Dog {name: "mimi", age: 12, sex: "公"}

class Animal {
 constructor(name, age) {
  console.log(new.target.prototype)
 }
 // 其他代码
 ...
}

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

 getName () {
  throw new Error('please overwrite getName method')
 }
}

class Dog extends Animal{
 constructor(name, age, sex) {
  super(name, age)
  this.sex = sex
 }
}

const pite = new Dog('pite', 2, '公')
a.getName()
// error
Uncaught Error: please overwrite getName method
  at Dog.getName (<anonymous>:8:11)
  at <anonymous>:1:3

class Animal {
 constructor(name, age) {
  // 如果 target 不是 基类 且 没有 getName 报错
  if (new.target !== Animal && !new.target.prototype.hasOwnProperty('getName')) {
   throw new Error('please overwrite getName method')
  }
  this.name = name
  this.age = age
 }
}

class Dog extends Animal{
 constructor(name, age, sex) {
  super(name, age)
  this.sex = sex
 }
}

const pite = new Dog('pite', 2, '公')
// error
Uncaught Error: please overwrite getName method
  at new Animal (<anonymous>:5:13)
  at new Dog (<anonymous>:14:5)
  at <anonymous>:1:1