JavaScript Class 的正确使用方法详解

class Person {
  // 构造函数
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }

  // 方法
  sayHello() {
    console.log(`Hello, my name is ${this.name} and I am ${this.age} years old.`);
  }

  // 静态方法
  static greet() {
    console.log("Hello!");
  }
}

// 创建实例
let person1 = new Person("Alice", 30);
person1.sayHello(); // 输出 "Hello, my name is Alice and I am 30 years old."

// 调用静态方法
Person.greet(); // 输出 "Hello!"

class Student extends Person {
  constructor(name, age, major) {
    // 调用父类的构造函数
    super(name, age);
    this.major = major;
  }

  study() {
    console.log(`${this.name} is studying ${this.major}.`);
  }

  // 重写父类的方法
  sayHello() {
    console.log(`Hello, my name is ${this.name}, I am ${this.age} years old, and I am studying ${this.major}.`);
  }
}

let student1 = new Student("Bob", 20, "Computer Science");
student1.sayHello(); // 输出 "Hello, my name is Bob, I am 20 years old, and I am studying Computer Science."
student1.study(); // 输出 "Bob is studying Computer Science."

class Circle {
  constructor(radius) {
    this._radius = radius; // 使用 _radius 作为内部属性
  }

  get radius() {
    return this._radius;
  }

  set radius(value) {
    if (value <= 0) {
      throw new Error("Radius must be positive.");
    }
    this._radius = value;
  }

  get area() {
    return Math.PI * this._radius * this._radius;
  }
}

let circle1 = new Circle(5);
console.log(circle1.radius); // 输出 5
console.log(circle1.area); // 输出 78.53981633974483

circle1.radius = 10;
console.log(circle1.radius); // 输出 10
console.log(circle1.area); // 输出 314.1592653589793

// circle1.radius = -1; // 抛出错误 "Radius must be positive."

class Counter {
  static count = 0;

  constructor() {
    Counter.count++;
  }

  static getCount() {
    return Counter.count;
  }
}

let counter1 = new Counter();
let counter2 = new Counter();
console.log(Counter.getCount()); // 输出 2