Prerequisites

• I have read the Contributing Guidelines.
• I agree to follow the Code of Conduct.
• I have searched for existing issues that already include this feature request, without success.

Describe the Feature Request

Add an ability to check whether the @event decorated property has any event listeners/subscribers.
There is currently no way to check if a callback function was assigned to this event prop.

Describe the Use Case

The original idea was to create a resuable component, containing a conditionally-rendered button as part of the component template outside of <slot>. The button needs to have an onClick action, but since it's inside the template, an @event decorator will be used on <Host> and we link onClick handler with action.emit().
But the conditional rendering has to be done with @Prop() hasAction:boolean
<SomeComponent hasAction={true} onAction={handler}/>

Describe Preferred Solution

A preferred solution would be to be able to check if the action has listeners/callback subscribed and based on that, render or hide the button in the template.

Angular offers this soluton using this.click.observers.length > 0

then the result with button would look like: <SomeComponent onAction={handler}/>
without button: <SomeComponent />

Describe Alternatives

An alternative could be a custom attribute added to the <Host> after rendering, e.g. reflect-event="action", which we could access via elementRef.
On the other hand it can be also done via children inside of , but then wiring between internal logic of and will be harder

Chromium Devtools offers node.eventListeners(); and getEventListeners(node), but of course it's not part of native DOM API.

Related Code

No response

Additional Information

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