js中的class

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

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

const person1 = new Person('Alice', 30);
person1.sayHello(); // 输出: Hello, my name is Alice and I am 30 years old.

class Student extends Person {
  constructor(name, age, grade) {
    super(name, age);
    this.grade = grade;
  }

  sayHello() {
    super.sayHello();
    console.log(`I am in grade ${this.grade}.`);
  }
}

class MathUtils {
  static PI = 3.14159;

  static calculateCircleArea(radius) {
    return this.PI * radius * radius;
  }
}

console.log(MathUtils.calculateCircleArea(5)); // 输出圆的面积