JavaScript 扩展类

使用JavaScript扩展类来增强原有的JavaScript类是一种常见的编程技巧。通过扩展类，开发者可以在不修改原有类的情况下，为其添加新的属性和方法，从而提供更多的功能和灵活性。在本文中，我们将介绍如何使用JavaScript扩展类，并提供一些实际案例代码来帮助读者更好地理解。

javascript
// 定义一个基类
class Animal {
  constructor(name) {
    this.name = name;
  }
  eat() {
    console.log(`${this.name} is eating.`);
  }
}
// 定义一个扩展类
class Cat extends Animal {
  constructor(name, color) {
    super(name);
    this.color = color;
  }
  meow() {
    console.log(`${this.name} is meowing.`);
  }
}
// 创建一个实例
const cat = new Cat('Tom', 'gray');
cat.eat();   // 输出：Tom is eating.
cat.meow();  // 输出：Tom is meowing.

javascript
// 定义一个基类
class Shape {
  constructor() {
    this.color = 'black';
  }
  draw() {
    console.log(`Drawing a shape with color ${this.color}.`);
  }
}
// 定义一个扩展类
class Circle extends Shape {
  constructor(radius) {
    super();
    this.radius = radius;
  }
  draw() {
    super.draw();
    console.log(`Drawing a circle with radius ${this.radius}.`);
  }
  calculateArea() {
    return Math.PI * this.radius * this.radius;
  }
}
// 创建一个实例
const circle = new Circle(5);
circle.draw();  // 输出：Drawing a shape with color black. Drawing a circle with radius 5.
console.log(`Area of the circle: ${circle.calculateArea()}`);

javascript
// 定义一个基类
class Animal {
  constructor(name) {
    this.name = name;
  }
  eat() {
    console.log(`${this.name} is eating.`);
  }
}
// 定义一个扩展类
class Cat extends Animal {
  constructor(name, color) {
    super(name);
    this.color = color;
  }
  meow() {
    console.log(`${this.name} is meowing.`);
  }
}
// 创建一个实例
const cat = new Cat('Tom', 'gray');
cat.eat();   // 输出：Tom is eating.
cat.meow();  // 输出：Tom is meowing.

javascript
// 定义一个基类
class Shape {
  constructor() {
    this.color = 'black';
  }
  draw() {
    console.log(`Drawing a shape with color ${this.color}.`);
  }
}
// 定义一个扩展类
class Circle extends Shape {
  constructor(radius) {
    super();
    this.radius = radius;
  }
  draw() {
    super.draw();
    console.log(`Drawing a circle with radius ${this.radius}.`);
  }
  calculateArea() {
    return Math.PI * this.radius * this.radius;
  }
}
// 创建一个实例
const circle = new Circle(5);
circle.draw();  // 输出：Drawing a shape with color black. Drawing a circle with radius 5.
console.log(`Area of the circle: ${circle.calculateArea()}`);