support for async callback

[francescoagati]

Hi,
there is a callback for async callback in map and other functions?

for example

$().ready(function () {
    $(".ss").asEventStream("click").map(function(e,cb) {
      setTimeout(function() {
          cb(5000)
       },1000);
    }).log();
});

function log should write 5000

[lautis]

You'll need to wrap your async callback as Bacon EventStream and then you can use flatMap to achieve this. FlatMap maps an event to a EventStream and merges the created streams to result stream.

$(".ss").asEventStream("click").flatMap(function(e) {
  return Bacon.later(1000, 5000);
});

There isn't a direct method to wrap callbacks, but if you're dealing with AJAX, Bacon.fromPromise can be used. If nothing else, you can always use a Bus.

stream.flatMap(function(e) {
  var bus = new Bacon.Bus()
  setTimeout(function() {
    bus.push(5000);
    bus.end()
  },1000);
  return bus;
});

[raimohanska]

@lautis thanks! Nice solution.

An even simpler solution to this particular problem would be

$(".ss").asEventStream("click").map(5000).delay(1000)

The flatMap solution is more flexible though. (Have a look at the implementation to delay to find out it actually just wraps your solution)

Would it make sense to include an easy callback wrapper API? If it existed, how would you like your client code to look like?

[raimohanska]

In fact, there is Bacon.fromCallback().

$(".ss").asEventStream("click").flatMap(function(v) {
  return Bacon.fromCallback(function(callback) {
    setTimeout(function() {
      callback(5000)
    }, 1000)
  })
})

Looks clumsy, of course, compared to the specific solution using delay.

[lautis]

Oh, cool. That's what I imagined the API for fromCallback to be. It's handy if you need to wrap a third party library to a Bacon stream (e.g. Zepto.js AJAX, which doesn't use promises).

[francescoagati]

thanks it really work like i want