JS Built-ins
← DesignPatterns1 / 25
DesignPatternsbeginner

Singleton — Static property

📖 Usage Example
class DB {
  static instance = null;
  static getInstance() {
    return DB.instance ?? (DB.instance = new DB());
  }
}
DB.getInstance() === DB.getInstance(); // true

Singleton ensures only one instance exists — getInstance always returns the same object.

Singleton Pattern — Static Property Approach

The Singleton pattern restricts a class to have only one instance. One common approach is using a static property to cache the instance.

Challenge: Implement a Database class with a static getInstance() method that returns the same instance every time it's called.

Example:

const db1 = Database.getInstance()
const db2 = Database.getInstance()
db1 === db2 // true
💡 Hints (3)
  • • Use a static property to store the instance
  • • Use the nullish coalescing operator (??)
  • • getInstance should check if instance exists before creating