@pandino/event-admin NPM

Event Admin

This is the reference implementation of the Pandino Event API.

Context

This package is part of the pandino-root monorepo. For detailed information about what is Pandino / how this package fits into the ecosystem, please consult with the related documentation(s).

Creating Events

Events consist of quite a lot of properties, therefore the easiest way to construct one is by utilizing the EventFactory. Sending the Event can be achieved by calling the postEvent() method on the obtained EventAdmin instance.

Every Event consists of a topic (string), and a properties object.

Please note, that Event delivery is fully async, and the order of delivery is not pre-defined!

It should be considered as a best practice to ensure that the properies objects is serializable. E.g.: JSON.stringify() and JSON.parse() compliant.

Example

import { EVENT_ADMIN_INTERFACE_KEY, EVENT_FACTORY_INTERFACE_KEY } from '@pandino/event-api';

export default class Activator {
  async start(context) {
    this.eventAdminReference = context.getServiceReference(EVENT_ADMIN_INTERFACE_KEY);
    this.eventAdmin = context.getService(this.eventAdminReference);
    this.eventFactoryReference = context.getServiceReference(EVENT_FACTORY_INTERFACE_KEY);
    this.eventFactory = context.getService(this.eventFactoryReference);

    // create the Event
    const event = eventFactory.build('@scope/app/TestTopic', {
      prop1: 'yayy',
    });
    
    // send the Event
    this.eventAdmin.postEvent(event);
  }

  async stop(context) {
    context.ungetService(this.eventFactoryReference);
    context.ungetService(this.eventAdminReference);
  }
}

Listening to Events

Any Service which implements the @pandino/pandino-event-admin/EventHandler interface and has the service property event.topics (either a single string, or an Array<string> can be provided as value) defined can listen to Pandino Events.

In order to narrow down unnecessary triggering of EventHandlers, an additional service property event.filter can be defined!

Example

import { EVENT_HANDLER_INTERFACE_KEY, EVENT_TOPIC } from '@pandino/event-api';

export default class BundleActivator {
  async start(context) {
    this.registration = context.registerService(EVENT_HANDLER_INTERFACE_KEY, new TestTopicEventHandler(), {
      [EVENT_TOPIC]: '@scope/app/TestTopic'
    });
  }

  async stop(context) {
    context.unregisterService(this.registration);
  }
}

class TestTopicEventHandler {
  handleEvent(event) {
    console.log(event.getTopic());
    console.log(event.getPropertyNames());
    // ...
  }
}

Topics

Topics should be unique. The recommended way of setting them up to prefix every topic with an actual package scope, and make them as explicit as possible. Topic segment separator MUST be the / character. Topics CAN start with the @ character to mirror NPM-style scopes, but it is not mandatory.

Topic matching

Matching by default is done in an case-sensitive, as-is manner for plain topics, e.g.: @scope/package/topic1. In this case, only exact matches will trigger listeners.

However there are two reserved keys which you can use as suffixes to loosen up the matching:

.: matches for exactly one additional segment, no more, no less
*: matches for at least one additional segment, no less

Examples

In the Table below headers represent topics, and the first column the test cases:

	@pandino/pandino/Foo	@pandino/pandino.	@pandino/pandino*
@pandino/pandino/Foo	true	true	true
@pandino/pandino/Bar	false	true	true
@pandino/pandino/Foo$1	false	true	true
@pandino/pandino/Foo/Test	false	false	true
@pandino/pandino	false	false	false