The Magic of Annotations

Decorators are a special @ syntax that let you " wrap " classes and their methods to add new behavior without modifying the original code. Think of them as reusable modifiers.

// Example of what decorators look like in practice:

@singleton  // Only one instance of this class can exist
@logged     // Log all method calls automatically
class UserService {
  @readonly   // This property cannot be changed after creation
  id = generateId();

  @memoize    // Cache the result of this method
  fetchUserData(userId) {
    return fetch('/api/users/' + userId);
  }
}

How Decorators Work

A decorator is simply a function that receives a class or method as its argument and returns a modified version:

function readonly(target, key, descriptor) {
  descriptor.writable = false;
  return descriptor;
}