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js实现class

2026-03-14 03:09:22JavaScript

实现类的基本语法

在JavaScript中，使用class关键字定义类。类可以包含构造函数、方法和属性。

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

  greet() {
    return `Hello, my name is ${this.name}`;
  }
}

const person = new Person('Alice', 25);
console.log(person.greet()); // 输出: Hello, my name is Alice

继承与扩展

通过extends关键字实现继承，子类可以覆盖或扩展父类的方法。

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

  study() {
    return `${this.name} is studying in grade ${this.grade}`;
  }
}

const student = new Student('Bob', 18, 12);
console.log(student.study()); // 输出: Bob is studying in grade 12

静态方法与属性

静态方法属于类本身而非实例，通过static关键字定义。

class MathUtils {
  static add(a, b) {
    return a + b;
  }

  static PI = 3.14159;
}

console.log(MathUtils.add(2, 3)); // 输出: 5
console.log(MathUtils.PI); // 输出: 3.14159

Getter 与 Setter

通过get和set定义属性的访问器，用于封装逻辑。

class Circle {
  constructor(radius) {
    this._radius = radius;
  }

  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  2;
  }
}

const circle = new Circle(5);
console.log(circle.area); // 输出: 78.53981633974483
circle.radius = 10;
console.log(circle.area); // 输出: 314.1592653589793

私有字段

使用#前缀定义私有字段，仅在类内部可访问。

class Counter {
  #count = 0;

  increment() {
    this.#count++;
  }

  getCount() {
    return this.#count;
  }
}

const counter = new Counter();
counter.increment();
console.log(counter.getCount()); // 输出: 1
// console.log(counter.#count); // 报错: Private field must be declared in class

类表达式

类可以通过表达式形式定义，适合动态生成类。

js实现class

const Animal = class {
  constructor(name) {
    this.name = name;
  }

  speak() {
    return `${this.name} makes a noise`;
  }
};

const dog = new Animal('Dog');
console.log(dog.speak()); // 输出: Dog makes a noise