Add onEvent callback to useEventSource

[KubaJastrz]

Adds a callback to event source stream, which fires whenever new data comes in. Useful if you don't want to merely display the latest message value, but rather do something with it. Like displaying a toast, computing a new state, analytics, you name it.

Usage:

useEventSource("/sse", {
    onEvent(data) {
        console.log(data);
    },
});

[sergiodxa]

This can easily be done with an effect in user-land:

let value = useEventSource("/sse");
useEffect(() => {
  // do something with `value`
}, [value])

[KubaJastrz]

That's only if the value has changed. I suppose it could be worked around by adding some unique identifier inside of the message.

[KubaJastrz]

@sergiodxa are you interested in adding this change?

[bitofbreeze]

@KubaJastrz @sergiodxa Could we extend useEventSource to allow reconnecting when the stream is closed? I don't see any way of currently doing this, and I think using a similar idea as here but making onEvent report disconnects too or adding perhaps an onError handler could make this possible.

For reference, here are the handlers partykit's websocket client hook exposes: