fromEvent on node.js events

[jfedyczak]

I'm trying to migrate from most.js. Is it possible to use fromEvent on node.js events? I'm trying to pass EventEmitter as a source but with no luck...

[Hypnosphi]

As stated in docs, fromEvent is suited for DOM events. It uses .addEventListener internally. fromNodeEvent could be implemented like this:

function fromNodeEvent(emitter, event) {
  let callback;
  return xs.create({
    start(listener) {
      callback = value => listener.next(value);
      emitter.addListener(event, callback);
    },
    stop() {
      emitter.removeListener(event, callback);
    }
  });
}

[jfedyczak]

Maybe such method should be added? It is present in most.js and in RxJS. I would provide a PR, but my TypeScript is not that fluent...

[staltz]

I think we could do this, since fromEvent is an extra, and size is not a concern, but parity with RxJS and most.js is a benefit.

[jfedyczak]

Thank you for the fix, but I'm trying to test this and I believe there's a problem with emitting events with more than one argument as in:

var fromEvent = require('xstream/extra/fromEvent').default
var http = require('http')

var srv = http.createServer()

fromEvent(srv, 'request')
.addListener({
  next: function(req, res) { // <-- problem here
      // res is undefined
      res.end(req.url)
  },
  error: function(err) { console.error(err) },
  complete: function() { console.log('completed') },
})

srv.listen(3002)

Possible solution would be emitting an array with all the args or passing all the args...

[staltz]

Yeah, it would have to be an array or an object.

[xtianjohns]

I sympathize with the use case there, @jfedyczak. I think implementations in other libraries handle this issue with selector support, which allows users to declare how to map the arguments from the emitter into the stream.

I'd be happy to take a stab at that, but I think it deserves a separate issue and maybe a discussion about how that approach fits in with the larger goals of xstream.