Lære Setters in Classes | Inheritance and Encapsulation

When you want to control how a property is set on an object, you can use a setter method in a JavaScript class. Setters use the set keyword followed by a method name, and are designed to execute code whenever a property is assigned a new value. This lets you validate, transform, or restrict values before they are actually stored. Setters are especially useful for encapsulation: they allow you to expose a property for assignment, but keep tight control over what values are accepted.

The set syntax looks similar to defining a method, but with the set keyword in front. Inside the setter, you typically store the value in a private or internal property (often with a leading underscore or, in later chapters, a private field). You can also add checks to ensure the value meets certain criteria before saving it, or transform it as needed.


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class Product {
  constructor(name, price) {
    this.name = name;
    this._price = price; // Internal property
  }

  get price() {
    return this._price;
  }

  set price(value) {
    // Validate that price is a positive number
    if (typeof value !== "number" || value < 0) {
      throw new Error("Price must be a non-negative number");
    }
    this._price = value;
  }
}

const item = new Product("Book", 15);
console.log(item.price); // 15

item.price = 25; // Uses the setter
console.log(item.price); // 25

// item.price = -10; // Would throw an error

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class Product {
  constructor(name, price) {
    this.name = name;
    this._price = price; // Internal property
  }

  get price() {
    return this._price;
  }

  set price(value) {
    // Validate that price is a positive number
    if (typeof value !== "number" || value < 0) {
      throw new Error("Price must be a non-negative number");
    }
    this._price = value;
  }
}

const item = new Product("Book", 15);
console.log(item.price); // 15

item.price = 25; // Uses the setter
console.log(item.price); // 25

// item.price = -10; // Would throw an error

Var alt klart?

Tak for dine kommentarer!

Sektion 2. Kapitel 6