Hooks

onTransform

This hook is called after the route has been matched and before the inputs are validated.

Decorate the Context

When you return an object from the hook, the object is merged into the context for subsequent hooks and handlers.

This is the main purpose of the onTransform hook.

const db = new SomeDatabase();

const depsPlugin = createApp()
  .decorate({
    db,
    userService: new UserService(db),
  })
  .onTransform(({ userService, request }) => {
    return {
      authService: new AuthService(userService, request),
    };
  })
  .export();

This is very similar to decorate, but decorate is only useful when you don't need the request context in your services.

onTransform is meant to be used to decorate the context with utilities and services that require knowledge of the request context.

Modify Inputs

You can also modify the request before inputs are validated.

const app = createApp().onTransform(({ params }) => {
  // replace "-" with undefined
  if (params.slug === "-") {
    params.slug = undefined;
  }
});

WARNING

Most validation libraries provide some way of "transforming" input values before the value is validated. I would recommend you use the validation library to accomplish this instead of modifying the inputs in a hook. It provides a consistent, easy way of modifying individual properites at any level of the request.

Short-circuiting

You can short-circuit the request life cycle by returning a Response object. All subsequent hooks and handlers will be skipped (except for onGlobalAfterResponse).

const authPlugin = createApp()
  .onTransform(() => {
    if (someCondition()) return new Response();

    // ...
  })
  .export();