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ng-event-bus

RxJS-based message/event bus service for Angular apps inspired by NgRadio. Inject it in your application module. You can check npm page.

Build status npm version

Installation

npm install --save ng-event-bus

Angular Compatibility Table

Angular version ng-event-bus version
18.x 7.x.x
17.x 6.x.x
16.x 5.1.x
15.x 5.0.x
15.x 5.0.x
14.x 4.x.x
13.x 4.x.x
12.x 3.x.x
11.x 2.x.x

Usage

First, import it:

import { NgEventBus } from 'ng-event-bus';

Then, inject it as a service (do not forget about providers) in your Angular application:

import { NgEventBus } from 'ng-event-bus';

@NgModule({
    imports:[
        ...
    ],
    providers: [
        ...,
        NgEventBus,
        ...
    ],

constructor(private eventBus: NgEventBus) { ... }

Since you have NgEventBus instance in your app, you can use these methods for passing messages:

  • this.eventBus.cast(key, data) - send a message to event bus.

  • this.eventBus.on(pattern) - returns observable you can subscribe to listen events.

Where:

  • key must be a string and must not be empty, otherwise it will throw an exception.
  • data is optional and can be any type of object.
  • pattern must be a string and must not be empty.

Patterns

Patterns may contain multiple segments split by :. Use this feature to create namespaces for messages you cast. You can use * in pattern to subscribe to any matching segment, or use ** to subscribe to all segments, starting from particular position.

For example, you can use on('error:*') and subscribe to all errors, including something like error:http or error:internal and so on:

this.eventBus.cast('app:start',     'started');
this.eventBus.cast('message:greet', 'Hi!');
this.eventBus.cast('message:bye',   'Bye!');

this.eventBus.on('app:start').subscribe((meta: MetaData) => {
    console.log(meta.data); // will receive 'started' only
});

this.eventBus.on('message:greet').subscribe((meta: MetaData) => {
    console.log(meta.data); // will receive 'Hi!'
});

this.eventBus.on('message:bye').subscribe((meta: MetaData) => {
    console.log(meta.data); // will receive 'Bye!'
});

this.eventBus.on('message:*').subscribe((meta: MetaData) => {
    console.log(meta.data); // will receive both 'Hi!' and 'Bye!'
});

this.eventBus.on('**').subscribe((meta: MetaData) => {
    console.log(meta.data); // will receive all messages: 'started', 'Hi!' and 'Bye!'
});

MetaData

When you subscribe to the observable, you can optionally get an instance of MetaData class. This instance contains information related to the emission of the event through the bus. The properties of this instance are:

  • id: A unique identifier of the message sent through the events bus.
  • key: Original key associated to the message.
  • data: Data associated to message. It's optional.
  • timestamp: Time in milliseconds in which the message was generated.
this.eventBus.cast('app:start', 'started');

this.eventBus.on('app:start').subscribe((meta: MetaData) => {
    console.log(meta.id);           // will print "d9c31eb0-b3f3-4764-a96d-6a703112a696"
    console.log(meta.key);          // will print "app:start"
    console.log(meta.data);         // will print "started"
    console.log(meta.timestamp);    // will print 1605934473553
});


this.eventBus.cast('message:bye', {message: 'bye'});

this.eventBus.on('**').subscribe((meta: MetaData) => {
    console.log(meta.id);           // will print "4945f28c-d2a5-4738-b7d1-f3df8f08422c"
    console.log(meta.key);          // will print "message:bye"
    console.log(meta.data);         // will print {message: 'bye'}
    console.log(meta.timestamp);    // will print 1605934709116
});

Examples

These strings will match:

  • on('**' ).suscribe can subscribe to any message with any segments count

  • on('a' ).suscribe can subscribe to cast('a', ...)

  • on('a:b' ).suscribe can subscribe to cast('a:b', ...)

  • on('a:b:c' ).suscribe can subscribe to cast('a:b:c', ...)

  • on('a:**' ).suscribe can subscribe to cast('a:b:c', ...), cast('a:b:c:d:e:f', ...)

  • on('a:*:*' ).suscribe can subscribe to cast('a:b:c', ...), cast('a:f:g', ...), cast('a:n:m', ...)

  • on('a:b:*' ).suscribe can subscribe to cast('a:b:c', ...), cast('a:b:d', ...), but not cast('a:b', ...)

  • on('a:b:**').suscribe can subscribe to cast('a:b:c',. ..)

  • on('*:b:*' ).suscribe can subscribe to cast('a:b:c', ...)

  • on('a:*:*' ).suscribe can subscribe to cast('a:b:c', ...)

Need to unsubscribe (observable)?

Yes, in the normal scenario usage it's necessary you unsubscribe from the observable to avoid memory leaks. That happens because the library exposes an infinite observable. That's no exactly related to the library, but in the way in which the observables work in RxJS.

However, there are ways that you don't need to unsubscribe, for example if you use .first() in the pipe of the observable because using this method would turn it into a finite observable (It would apply in your case if you're just waiting for a one-time event).

I recommend you to read this stackoverflow answer about a similar question.

Release history & changelog

See the Releases page for a list of all releases, including changes.

Help / Support

If you run into any issues, please email me at [email protected] or you can use the contact form in my page.

For bug reports, please open an issue on GitHub.

Contributing

  1. Fork it.
  2. Create your feature branch (git checkout -b my-new-feature).
  3. Commit your changes (git commit -am 'Added some feature').
  4. Push to the branch (git push origin my-new-feature).
  5. Create a new Pull Request.

License

MIT