ES6 继承例子：

class Child extends Parent {
  constructor(firstName,lastName,age) {
    super(firstName,lastName)
    this.age = age
  }
}

ES5的等价写法：

function Child(firstName,age) {
  Parent.call(this,firstName,lastName)
  this.age = age
}
Child.prototype = Object.create(Parent.prototype)

Child.constructor = Child