Better error messages when an @Output property is not initialized.

Related: #3754 (should be fixed together)

Listing an event in a directive without creating an associated EventEmitter instance results in cryptic error:

TypeError: Cannot read property 'observer' of undefined
at Function.ObservableWrapper.subscribe (angular2.js:19403)
at EventEmitterAccessor.subscribe (angular2.js:26062)
at AppViewManagerUtils._setUpEventEmitters (angular2.js:20932)
at AppViewManagerUtils._hydrateView (angular2.js:20896)
at AppViewManagerUtils.hydrateRootHostView (angular2.js:20814)
at AppViewManager.createRootHostView (angular2.js:23990)
at angular2.js:13594
at Zone.run (zone.js:113)
at Zone.run (angular2.js:12928)
at zoneBoundFn (zone.js:86)

To reproduce:

@Directive({
    selector: '[foo]'
})
class Foo {
  @Output() foo; // not initialized to = new EventEmitter();
}

fix(ElementInjector): better error message for events with no EventEm…

Is this still an issue? Can you fix it?

Yes I also got this cryptic error message. I am going to try to fix this one.

When subscribing to the non initialized EventEmitter in the template eg:

    <editor (submitted)="onReply()"></editor>
   // with 
      @Output() submitted;

The error message is also not very precise as of where the error is coming from.

core.es5.js:1084 ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'subscribe' of undefined
TypeError: Cannot read property 'subscribe' of undefined

@mhevery

Hi @mhevery @vicb
I submitted a PR for this issue some time ago. I just fixed a conflict, lint errors and tests. See #19116

Please let me know if there is something I can do. Cheers!

@pkozlowski-opensource

@pkozlowski-opensource Is the issue relevant?
Will this pull request be accepted?
#19116

@output

fix(core): throw error message when @output not initialized

@output

For me the error stopped when I changed the import statement from import { EventEmitter } from 'events'; to import { EventEmitter } from '@angular/core'. The first option was suggested by angular as default but I think that the second one should be used. Everything works fine now after I changed it.

Example:
@output() variableToEmit: EventEmitter = new EventEmitter();

showsString(text: any) {
this.variableToEmit.emit(text);
}

Hope that helps .

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Better error messages when an `@Output` property is not initialized. #3664

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Better error messages when an @Output property is not initialized. #3664

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mhevery commented on Jul 1, 2016

11 remaining items

ashish173 commented on Jan 19, 2017

cedvdb commented on Apr 16, 2017

aldo-roman commented on Jan 16, 2018

splincode commented on Jul 26, 2018

luisfelix199276 commented on Nov 20, 2018

angular-automatic-lock-bot commented on Sep 14, 2019

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Better error messages when an `@Output` property is not initialized. #3664