retrieval.md

Dependency Retrieval

Retrieve dependencies from the container using type-safe methods.

get(key)

Retrieve a dependency from the container. Searches parent containers if not found locally. Returns undefined if not found.

For singleton registrations (class or instance), returns the cached instance on subsequent calls.

const value = container.get('apiUrl');
const userService = container.get(UserService);

// Factory registrations return a new instance each time
const timestamp1 = container.get('timestamp');
const timestamp2 = container.get('timestamp');
// timestamp1 !== timestamp2

require(key)

Retrieve a dependency, or throw an error if the dependency is not found in the container hierarchy.

try {
  const config = container.require('appConfig');
}
catch (error) {
  console.error('Required dependency not found:', error.message);
}

This is useful when you want to ensure a dependency exists and fail fast if it doesn't.

has(key)

Check if a dependency exists in the container or any parent container.

if (container.has('logger')) {
  const logger = container.get('logger');
}

This allows you to conditionally retrieve dependencies or provide fallback behavior.