Target wrapper

provideCraftTargetWrapper wraps the registration of every Craft component or directive created in the current injector, giving you a hook at the moment each one comes to life.

Use it when you need to observe or enrich target registration across a subtree: a specialised registry, observability, host names decorated with tags. Not when you just need a parent to drive its children — craftRegisterFor is built on this and already does it.

Dependency injection here is not type-checked

The callback runs in a runtime chain, outside the usual DI inference. A service that is not provided in the current injector fails at runtime, and the wrapper's type cannot catch it. That is why the first argument is a mandatory warning string.

The common case

import { provideCraftTargetWrapper } from '@craft-ng/core';

const provideTargetCustomization = provideCraftTargetWrapper(
  'Warning: dependency injection here is not type-safe and may fail at runtime',
  function* (context, next) {
    return yield* next();
  },
);

The callback is a generator, so it can yield a Craft service:

const provideTargetAudit = provideCraftTargetWrapper(
  'Warning: dependency injection here is not type-safe and may fail at runtime',
  function* (context, next) {
    const audit = yield* TargetAuditService();
    audit.recordCreatedTarget(context.kind, context.name);

    return yield* next();
  },
);

The context

type CraftTargetContext = {
  target: unknown;
  kind: 'component' | 'directive';
  name: string;
  ref: unknown;
  hostName: string;
  injector: Injector;
};

target, kind, name and ref describe the real instance and are immutable. hostName is the only field you can change, by passing it to next(...).

Tagging the host name

import { HOST_TAG_LIST, provideCraftTargetWrapper } from '@craft-ng/core';

const provideTagBasedTargetRegistration = provideCraftTargetWrapper(
  'Warning: dependency injection here is not type-safe and may fail at runtime',
  function* (context, next) {
    const tags = context.injector.get(HOST_TAG_LIST, []);
    const hostName =
      tags.length === 0
        ? context.hostName
        : `${tags.join('/')}/${context.hostName}`;

    return yield* next({ hostName });
  },
);

Install it in the component's scope:

const RegisterForDemo = craftComponent(
  'RegisterForDemo',
  {
    providers: [provideTagBasedTargetRegistration],
  },
  // ...
);

Order matters — a wrapper that modifies the hostName a registry consumes must be declared before that registry's wrapper:

providers: [
  provideTagBasedTargetRegistration,
  provideRegisterForCounter(),
],

Wrappers chain in declaration order; the first is the outermost, exactly like provideFnWrapper.

next() and cleanup

next() continues the chain and returns a release function, because the wrappers after yours may have added a registration or a resource of their own.

A wrapper that only adapts the hostName just delegates:

function* wrapper(context, next) {
  return yield* next({ hostName: `tag:${context.hostName}` });
}

A wrapper that creates its own resource must combine both cleanups:

const provideObserver = provideCraftTargetWrapper(
  'Warning: dependency injection here is not type-safe and may fail at runtime',
  function* (context, next) {
    const releaseNext = yield* next();
    const releaseObserver = observeTarget(context);

    return () => {
      releaseObserver();
      releaseNext();
    };
  },
);

The runtime calls the cleanup automatically when the component's injector is destroyed. For a directive, it runs when the rendered node is removed.

Pitfalls

Dropping the release function from next(). Everything registered further down the chain then leaks. Always return it, alone or combined with your own.

Declaring the wrapper after the registry it should influence. The registry will have already consumed the unmodified hostName.

Assuming a yielded service exists. Nothing checks it here — a missing provider is a runtime failure.

Building a specialised registry

A registry can use the wrapper directly, without depending on craftRegisterFor:

const provideSpecializedRegistry = provideCraftTargetWrapper(
  'Warning: dependency injection here is not type-safe and may fail at runtime',
  function* (context, next) {
    const registry = yield* SpecializedRegistry();
    const releaseNext = yield* next();
    const releaseRegistry = registry.add({
      kind: context.kind,
      name: context.name,
      ref: context.ref,
      hostName: context.hostName,
    });

    return () => {
      releaseRegistry();
      releaseNext();
    };
  },
);

This is how you build registries by tag, by component kind, by scope or by business need, while reusing the same lifecycle as craftRegisterFor.

See Also

• craftRegisterFor — the built-in registry on top of this
• Observability