如何重写构造函数？

function MyClass(name, age) {
  this.name = name;
  this.age = age;
}

MyClass.prototype.sayHello = function() {
  console.log("Hello, " + this.name + "!");
};

function SubClass(name, age, gender) {
  // 调用父类的构造函数
  MyClass.call(this, name, age);
  
  this.gender = gender;
}

// 继承父类的原型
SubClass.prototype = Object.create(MyClass.prototype);
SubClass.prototype.constructor = SubClass;

SubClass.prototype.sayGender = function() {
  console.log("I am " + this.gender + ".");
};

var obj = new SubClass("Alice", 25, "female");
obj.sayHello(); // 输出 "Hello, Alice!"
obj.sayGender(); // 输出 "I am female."