Event Listener

An event can have multiple event listeners, which execute using the onion model

Create Event Listener

For example, create an Event Listener echo in the module demo-student. When responding to an event, add a ! suffix to the event parameter Hello World and pass the new parameter to the next method.

1. Cli command

$ vona :create:bean eventListener echo --module=demo-student

2. Menu command

TIP

Context Menu - [Module Path]: Vona Bean/Event Listener

Event Listener Definition

1. Automatically Generated Code Skeleton

type TypeEventData = unknown; // TypeEventEchoData;
type TypeEventResult = unknown; // TypeEventEchoResult;

@EventListener({ match: 'some-module:echo' })
export class EventListenerEcho
  extends BeanBase
  implements IEventExecute<TypeEventData, TypeEventResult>
{
  async execute(
    _data: TypeEventData,
    next: NextEvent<TypeEventData, TypeEventResult>,
  ): Promise<TypeEventResult> {
    // next
    return next();
  }
}

• TypeEventData: Defines the parameter type
• TypeEventResult: Defines the result type
• match: Specifies the events to listen for

Name	Type	Description
match	string|regexp|(string|regexp)[]	Specifies the events to listen for

2. Adjust the code

+ import type { TypeEventEchoData, TypeEventEchoResult } from './event.echo.ts';

+ type TypeEventData = TypeEventEchoData;
+ type TypeEventResult = TypeEventEchoResult;

+ @EventListener({ match: 'demo-student:echo' })
export class EventListenerEcho
  extends BeanBase
  implements IEventExecute<TypeEventData, TypeEventResult> {
+ execute(data: TypeEventData, next: NextEventSync<TypeEventData, TypeEventResult>): TypeEventResult {
+   const dataNew = `${data}!`;
    // next
+   return next(dataNew);
  }
}

• TypeEventData: Defines the parameter type
• TypeEventResult: Defines the result type
• match: Specifies the event name to listen for, demo-student:echo
• execute: To support both asynchronous and synchronous events, it's changed to a synchronous method
  • next: The type is changed to NextEventSync
• dataNew: Generate new event parameter value ​​and pass it to the next method

Event Listener Order

Multiple Event Listeners can be associated with the same event. Therefore, VonaJS provides two parameters to control the execution order of Event Listeners.

1. dependencies

For example, given an Event Listener demo-student:echo3, we want the execution order to be: demo-student:echo3 > Current

@EventListener({
  match: 'demo-student:echo',
+ dependencies: 'demo-student:echo3',
})
class EventListenerEcho {}

2. dependents

The order of dependents is exactly the opposite of dependencies. We want the execution order to be: Current > demo-student:echo3

@EventListener({
  match: 'demo-student:echo',
+ dependents: 'demo-student:echo3',
})
class EventListenerEcho {}

Event Listener Enable/Disable

You can control enable/disable of Event Listeners.

1. Enable

src/backend/config/config/config.ts

// onions
config.onions = {
  eventListener: {
    'demo-student:echo': {
+     enable: false,
    },
  },
};

2. Meta

Allows Event Listeners to take effect in a specified operating environment.

Name	Type	Description
flavor	string|string[]	See: Runtime Environments and Flavors
mode	string|string[]	See: Runtime Environments and Flavors

• Example

@EventListener({
+ meta: {
+   flavor: 'normal',
+   mode: 'dev',
+ },
})
class EventListenerEcho {}

Inspect

You can directly inspect the currently effective event listener list.

class ControllerStudent {
  @Web.get('test')
  test() {
+   this.bean.onion.eventListener.inspectEventListener('demo-student:echo');
  }
}

• this.bean.onion: Get the global Service instance onion
• .eventListener: Get the Service instance related to the Event Listener
• .inspectEventListener: Output the list of currently effective Event Listeners, passing in the event name demo-student:echo

When accessing the test API, the list of currently effective Event Listeners will be automatically output to the console, as shown below: