Installation
npm install @brainhubeu/hadron-events --save
More info about installation
Overview
Event Manager is a tool which allows manipulating Hadron's default behavior without the need to change the code base. It can be achieved via custom listeners defined by the developer. There are a bunch of extension points spread all over the hadron framework where listeners can be hooked up.
Initializing
Pass package as an argument for hadron bootstrapping function:
const hadronEvents = require('@brainhubeu/hadron-events');
hadron(expressApp, [hadronEvents], config).then(() => {
console.log('Hadron with eventManager initialized');
});
After initialization you can retrieve event manager from DI container - it is registered under the key eventManager
.
Event Manager methods
Registering listeners for events
eventManager.registerEvents(listeners);
listeners
- an array of objects which have to follow convention showed below:
{
name: 'string',
event: 'string',
handler: 'function'
}
Example:
const config = {
events: {
listeners: [
{
name: 'Listener1',
event: 'createRoutesEvent',
handler: (callback, ...args) => {
const myCustomCallback = () => {
console.log("Hey! I've changed the original hadron function!");
return callback(...args);
};
return myCustomCallback();
},
},
{
name: 'Listener2',
event: 'myCustomEvent',
handler: (callback, ...args) => {
const myCustomCallback = () => {
console.log('My custom event!');
return callback(...args);
};
return myCustomCallback();
},
},
],
},
};
hadron(app, [hadronEvents], config).then((container) => {
container.take('eventManager').emitEvent('myCustomEvent');
});
Emitting events
eventEmitter.emitEvent(eventName);
Calls all listeners handlers registered for the event with event name passed to it.
eventName
- name of the event which will be fired
Listeners
You can create your listeners in the main config file.
As a first argument listener's handler method will receive a callback function originally called by hadron, so you can change/override it however you want and then return a call of newly created function or a call of existing callback if you don't want to change it.
To be able to receive callback mentioned above, the first argument should be named exactly callback
, otherwise, you will not receive the callback.
You can also, define your listener's handler without callback
argument or even without any arguments, which is also a valid way to create listeners, you just won't be able to access the callback.
The second argument of listeners handler method is ...args
, which can be used as arguments for the callback function.
An example of a listener:
{
name: 'Listener',
event: 'createRoutesEvent',
handler: (callback, ...args) => {
const myCustomCallback = () => {
console.log("Hey! I've changed the original hadron function!");
return callback(...args);
}
return myCustomCallback();
}
}
Extension points in hadron
As said before, there are a couple of extension points in the hadron framework to which you can hook up your listeners.
The extension depends from packages that You are using and are listed below:
--- hadron-express
HANDLE_REQUEST_CALLBACK_EVENT
Event fires, before route callback function is called, passes route callback to the listener.
Example:
const ExpressEvent = require('@brainhubeu/hadron-express').Event;
const listeners = [
{
name: 'Listener',
event: ExpressEvent.HANDLE_REQUEST_CALLBACK_EVENT,
handler: (callback, ...args) => {
console.log('Request Handled!');
callback(...args);
},
},
];
HANDLE_TERMINATE_APPLICATION_EVENT
Event fires when the application is terminated with CTRL + C, passes default hadron callback to the listener.
const Event = require('@brainhubeu/hadron-events').Event;
const listeners = [
{
name: 'Listener',
event: Event.HANDLE_TERMINATE_APPLICATION_EVENT,
handler: () => {
console.log('Application is going to close');
},
},
];