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javascriptdomdom-eventscustom-element

Detect event listener from custom element (emitting events lazily)

I am writing a custom element and I want to periodically emit an event. Emitting the event requires some work, so I was thinking maybe I can be lazy and only emit the event (and do the work) if there is a listener.

Is it possible to detect that someone is listening to an event (non bubbling)? And in that case start emitting, until the listener is removed.

Or will the Javascript runtime be smart enough to not run the interval (where the only side effect is creating an event) when there is no listener?

Solution

  • With Javascript standard events, it appears you can't (unless you override the registration mechanism).

    But with custom registering and callback methods, you can achieve this by implementing the Observer pattern.

    Anyway, it you're lazy maybe it's easier to send useless events :-)