Getters and Setters

Example

class CartItem {
  private _qty = 1;

  constructor(public name: string, public unitPrice: number) {}

  get qty(): number {
    return this._qty;
  }

  set qty(value: number) {
    if (!Number.isInteger(value) || value < 1 || value > 10) {
      throw new RangeError("Quantity must be 1 to 10");
    }
    this._qty = value;
  }

  get lineTotal(): number {
    return this.unitPrice * this._qty;
  }
}

const item = new CartItem("Mango Box", 450);
item.qty = 3;
console.log(item.qty, item.lineTotal);
try {
  item.qty = 25;
} catch (e) {
  console.log((e as Error).message);
}

Output

3 1350
Quantity must be 1 to 10

Example

A property with only get cannot be assigned (TS2540).

class Circle {
  constructor(private r: number) {}
  get area(): number { return Math.PI * this.r ** 2; }
}

const c = new Circle(2);
c.area = 10;

Compiler output (tsc)

Line 7: error TS2540: Cannot assign to 'area' because it is a read-only property.