Hierarchy Injection

Injectors can form parent-child relationships, enabling modular and scoped dependency management.

Creating Child Injectors

Two ways to create a child injector:


// Method 1: Using createChild
const parentInjector = new Injector([[PlatformService]]);
const childInjector = parentInjector.createChild([[OrderService]]);
 
// Method 2: Pass parent to constructor
const childInjector = new Injector([[OrderService]], parentInjector);

Dependency Lookup

When a child injector can’t find a dependency, it automatically looks in its parent:


const parentInjector = new Injector([[PlatformService]]);
const childInjector = parentInjector.createChild([[OrderService]]);
 
// PlatformService is found in parent and returned
childInjector.get(PlatformService);

Controlling Lookup Behavior

Use decorators to control where dependencies are resolved:

Decorator	Behavior
`@Self()`	Only look in current injector
`@SkipSelf()`	Skip current, start from parent


class ChartComponent {
  constructor(
    // Must be in current injector
    @Self() @Inject(Container) private selfContainer: Container,
 
    // Must be in parent injector
    @SkipSelf() @Optional(Container) private parentContainer?: Container
  ) {}
}

Combine @SkipSelf() with @Optional() to gracefully handle cases where a parent dependency might not exist.