Prototype

Delegates object creation to the object itself via a clone() method. Useful when construction is expensive or complex and variations of an existing object are needed.

When to Use

• Object creation is expensive (DB reads, network calls, heavy computation) and cloning is cheaper
• You need many objects that are slight variations of a base object
• Classes to instantiate are specified at runtime
• Avoid subclassing just to configure an object

How to Apply

1. Create a Cloneable / Prototype interface with a clone() method
2. Implement clone() in each concrete class (copy all fields; deep-copy mutable nested objects)
3. Optionally maintain a prototype registry (Map<string, Prototype>) for named prototypes
4. Clients call clone() instead of new

Example

interface Prototype<T> { clone(): T; }

class Shape implements Prototype<Shape> {
  constructor(
    public color: string,
    public x: number,
    public y: number,
  ) {}

  clone(): Shape { return new Shape(this.color, this.x, this.y); }
}

// Cheap variant creation
const base = new Shape('red', 0, 0);
const copy = base.clone();
copy.x = 10;   // base is unaffected

References

• refactoring.guru/design-patterns/prototype