# EventAggregator inside Service without a View Not Working

**URL:** <https://discourse.aurelia.io/t/eventaggregator-inside-service-without-a-view-not-working/2087>\
**Category:** Help Requests\
**Created:** [January 5, 2019, 1:47pm UTC](https://discourse.aurelia.io/t/eventaggregator-inside-service-without-a-view-not-working/2087 "2019-01-05T13:47:26Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![kimgeorge](https://avatars.discourse-cdn.com/v4/letter/k/4af34b/32.png) [@kimgeorge](https://discourse.aurelia.io/u/kimgeorge)\
**Post date:** [January 5, 2019, 1:47pm UTC](https://discourse.aurelia.io/t/eventaggregator-inside-service-without-a-view-not-working/2087/1 "2019-01-05T13:47:26Z")

</div>

I’m trying to create a service which subscribes to an event and fires whenever the event occurs. I’m able to get the whole thing working if I create an empty view template for the service and put the subscription in the attached() function.

However if there is no view template, there’s no attached function called and I need to register the subscription somewhere. I tried creating the following class:

**service.js**

```javascript
import {inject} from 'aurelia-framework';
import {EventAggregator} from 'aurelia-event-aggregator';

@inject(EventAggregator)

export class Service {

  constructor(EventAggregator) {
    this.ea = EventAggregator;
  }

  registerSubscription = () =>
  {
    let subscription = this.ea.subscribe('someEvent', () => {
      console.log('Service triggered');
    });
  }
}

```

And registering the subscription in the constructor of the app:  
**app.js:**

```javascript
import {Service} from './modules/test/services/service'

export class App {
  constructor() {
    this.service = new Service;
    this.service.registerSubscription()
  }
}

```

> Message: Cannot read property ‘subscribe’ of undefined  
> Inner Error Stack:  
> TypeError: Cannot read property ‘subscribe’ of undefined  
> at Service.registerSubscription (webpack-internal:///+xuG:16:33)  
> at new App (webpack-internal:///app:7:16)  
> at Object.invoke (webpack-internal:///3U8n:464:12)

If I can’t register it here, do you have any suggestions of where I could register it? I also tried registering it in a method of the same class which I call in the classes constructor and I get the same error.

---

<div class="post-metadata">

**Author:** ![bigopon](https://yyz1.discourse-cdn.com/flex027/user_avatar/discourse.aurelia.io/bigopon/32/18_2.png) [@bigopon](https://discourse.aurelia.io/u/bigopon)\
**Post date:** [January 5, 2019, 5:40pm UTC](https://discourse.aurelia.io/t/eventaggregator-inside-service-without-a-view-not-working/2087/2 "2019-01-05T17:40:29Z")

</div>

The error is because the way you constructed your `Service` instance. When doing `new Service`, you didn’t give it the necessary instance of `EventAggregator`. What you should do is to use dependency injection for `Service` like following block:

```auto
@inject(Service)
export class App {
  constructor(service) {
    this.service = service;
    service.registerSubscription();
  }
}

```

---

<div class="post-metadata">

**Author:** ![kimgeorge](https://avatars.discourse-cdn.com/v4/letter/k/4af34b/32.png) [@kimgeorge](https://discourse.aurelia.io/u/kimgeorge)\
**Post date:** [January 7, 2019, 2:37am UTC](https://discourse.aurelia.io/t/eventaggregator-inside-service-without-a-view-not-working/2087/3 "2019-01-07T02:37:22Z")

</div>

Excellent it’s working now thanks!

For services that consume events like this, is registering it in the App constructor the best approach or is there some other pattern that makes more sense?