Lifecycle Hooks

An environment loader has a lifecycle that starts each time the load() method is invoked. Each lifecycle ends when the method returns. Your implementation can use lifecycle hook methods to tap into key events in the environment loader service.

Respond to events in the lifecycle of the loader by implementing one or more of the lifecycle hook interfaces presented. The hooks give you the opportunity to act on the instance at the appropriate moment.

Each interface defines the prototype for a single hook method, whose name is the interface name starting in lowercase. For example, the OnBeforeLoad interface has a hook method named onBeforeLoad().

You don't have to implement all (or any) of the lifecycle hooks, just the ones you need.

Interface	Lifecycle event
OnBeforeLoad	Before start the environment sources load
OnBeforeSourceLoad	Before a source starts to load the properties
OnBeforeSourceAdd	Before a source properties are added to the environment
OnAfterSourceAdd	After a source properties are added to the environment
OnAfterSourceComplete	After a source completes
OnAfterSourceError	After a source is rejected
OnAfterComplete	After all environment sources completes
OnAfterLoad	After the load is resolved
OnAfterError	After the load is rejected

Use cases

Below are examples of the expected behavior with the default loader implementation.

Table of Contents

1. Add logs to the loader
2. Resolve when setting a subset of properties
3. Stop loading after load error

Add logs to the loader

class Loader
  extends EnvironmentLoader
  implements
    OnAfterLoad,
    OnAfterComplete,
    OnAfterError,
    OnAfterSourceAdd,
    OnAfterSourceComplete,
    OnAfterSourceError,
    OnBeforeLoad,
    OnBeforeSourceAdd,
    OnBeforeSourceLoad
{
  constructor(
    protected override service: EnvironmentService,
    protected override sources?: ArrayOrSingle<LoaderSource>
  ) {
    super(service, sources);
  }
  onAfterLoad(): void {
    console.log('onAfterLoad');
  }
  onAfterComplete(): void {
    console.log('onAfterComplete');
  }
  onAfterError<E extends Error>(error: E): void {
    console.log('onAfterError', error);
  }
  onAfterSourceAdd(properties: EnvironmentState, source: LoaderSource): void {
    console.log('onAfterSourceAdd', properties, source);
  }
  onAfterSourceComplete(source: LoaderSource): void {
    console.log('onAfterSourceComplete', source);
  }
  onAfterSourceError(error: Error, source: LoaderSource): void {
    console.log('onAfterSourceError', error, source);
  }
  onBeforeLoad(): void {
    console.log('onBeforeLoad');
  }
  onBeforeSourceAdd(properties: EnvironmentState, source: LoaderSource): void {
    console.log('onBeforeSourceAdd', properties, source);
  }
  onBeforeSourceLoad(source: LoaderSource): void {
    console.log('onBeforeSourceLoad', source);
  }
}

Resolve when setting a subset of properties

class Loader extends EnvironmentLoader implements OnAfterSourceAdd {
  requiredProperties: Path[] = ['user.name', 'baseURL'];

  constructor(
    protected override service: EnvironmentService,
    protected override sources?: ArrayOrSingle<LoaderSource>,
    protected readonly query: EnvironmentQuery
  ) {
    super(service, sources);
  }

  onAfterSourceAdd(): void {
    if (this.query.containsAll(...this.requiredProperties)) {
      this.resolveLoad();
    }
  }
}

Stop loading after load error

class Loader extends EnvironmentLoader implements OnAfterError {
  constructor(
    protected override service: EnvironmentService,
    protected override sources?: ArrayOrSingle<LoaderSource>
  ) {
    super(service, sources);
  }

  onAfterError(): void {
    this.onDestroy();
  }
}