Event handlers
Falcon Server uses asynchronous events to notify about internal processes. With event handlers you are able to "hook" into particular place in order to modify Falcon Server's behavior or modify particular thing.
You can find available list of events here
Usage
In order to handle event fired by Falcon Server you need to use @eventHandler() decorator and extend EventHandlerBase class which requires you to implement execute method.
Then it needs to exported by Falcon Module.
The snipped below shows how to do that:
const { eventHandler, EventHandlerBase, Events } = require('@deity/falcon-server-env');
// custom event handler that processes errors
@eventHandler(Events.ERROR)
export class CustomErrorHandler extends EventHandlerBase {
async execute(error) {
// log error onto console
console.error(error);
}
}
Due to nature of Data Sources which are instantiated per each request we don't advise to watch for events from Data Source because each request will create instance of event handler.
Firing custom events
Besides events that Falcon Server emits you can also emit your own events. To do so, you need to inject EventEmitter2 to your class and simply fire event as you wish.
const { injectable } = require('inversify');
const { DataSource } = require('apollo-datasource');
const { EventEmitter2 } = require('eventemitter2');
@injectable()
export class CustomDataSource extends DataSource {
constructor(@inject('EventEmitter2') eventEmitter: EventEmitter2) {
super();
this.eventEmitter = eventEmitter;
}
async someResolver(obj, params, context, info) {
// something happened - trigger event
this.eventEmitter.emit('custom-event-name', 'arg1', 'arg2');
// or trigger it in async way
await this.eventEmitter.emitAsync('custom-event-name', 'arg1', 'arg2');
return {};
}
}
Available events
You can import Events enum available in @deity/falcon-server-env package to have list of predefined events:
const { Events } = require('@deity/falcon-server-env');
ERROR
Fired when Falcon Server catches global error
Parameters:
Errorinstance
BEFORE_INITIALIZED
Fired before initialization of the instance of Falcon Server (at the beginning of FalconServer.initialize() method). This event is fired before Falcon Server is configured with basic things so it can be used to execute some logic at the very beginning of Falcon Server lifetime.
Parameters:
FalconServerclass instance
AFTER_INITIALIZED
Fired after initialization of the instance of Falcon Server (at the end of FalconServer.initialize() method). This event is fired after everything that Falcon Server uses is initialized so it can be used to access all Falcon Server's internals.
Parameters:
FalconServerclass instance