Javascript Programming Tutorials, Guides & Best Practices

class Rectangle {
  constructor(width, height) {
    this.width = width;
    this.height = height;
  }

  get area() {
    return this.width * this.height;
  }

  set width(value) {
    if (value <= 0) throw new Error("Width must be positive");
    this._width = value;
  }

  get width() {
    return this._width;
  }
}

const rect = new Rectangle(10, 5);
console.log(rect.area); // Output: 50
rect.width = 15;
console.log(rect.area); // Output: 75

Let's put everything together by building a simple application using classes. We'll create a Book class and a Library class to manage a collection of books.