JavaScript: resolve next event as a promise
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JavaScript: resolve next event as a promise
For the purpose of testing, I want somehow to wrap events into promises(it's easier to wait for a promise resolution in mocha). So, I write something like:
const collectEvents = (eventEmmiter, eventName, count=1) =>
return new Promise((resolve) =>
const result =
const listener = (msg) =>
result.push(msg)
if(result.length === count)
resolve(result)
eventEmmiter.removeListener(eventName, listener)
eventEmmiter.on(eventName, listener)
)
and use it like this:
Promise.all([
collectEvents(client1, 'message'),
collectEvents(client2, 'message')
]).then(
it works, but I feel like I invented the wheel again. Did I? is there a standard way to achieve the behavior?
eventEmitter.on("error", reject)
removeListener
in this particular case, a client provides an "error" event; But there is no specification about the "error" event in general.
– kharandziuk
Aug 9 at 14:26
True, although all standard streams I've seen so far provide an error event. Sure, it's not codified, and that's why there is no standard promisification utility either - everyone needs it to behave a little differently. Consider also the case that the stream ends before emitting
count events - would you want to reject then?– Bergi
Aug 9 at 15:00
count
>would you want to reject then? it's also a kinda question which I don't want to answer:) I use the function for testing. So, I rely on mocha timeouts in the case
– kharandziuk
Aug 9 at 15:17
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I would add an
eventEmitter.on("error", reject)(and the respectiveremoveListener) but apart from that it looks totally fine. No, the standard library doesn't provide such a utility yet afaik.– Bergi
Aug 9 at 13:52