Support node-style callbacks

[abesto]

Hey! I started playing with Bacon after attending your workshop at mloc.js. I really like it so far. Here's one addition I'd find useful: support for Node.js-style callbacks. This makes bacon.js much easier to use on the server side.

I realize that this is a bit like the jQuery adapter so maybe it should be in a separate package, but the readme explicitly mentions that bacon.js works fine on the server; this looks like a basic requirement for node.js usage.

Hope you like the idea; please give feedback on the implementation if you'd prefer some other solution :)

Keep up the great work! 👍

[raimohanska]

Looks good!

Could you give a couple of "real-life" examples of the usage?

[abesto]

tl;dr Using the Redis client library

Of course. Here's one where I use it: https://github.com/abesto/shopping-list/blob/master/routes/tab.js

This is basically an end-point of a REST API. Walking through the create method line by line (assume redis is a redis client instance):

1. increase the "next free id" of the resource, pass on the last value (this will be the id of the object we create now)
2. generate the redis key to the newly created object (includes the id we just got back from redis)
3. create the object data based on the id from redis and the request
4. write the data to redis (Bacon.redis is a helper function to create partial functions useful in .flatMapLatest
5. add the newly created object to the list of known objects
6. respond to the client. note how Bacon.Observable.prototype.respond (another helper) is the only place where we have explicit error handling. bacon.js extended with fromNodeCallback hides explicit node-style error handling similarly to the Either monad in Haskell (if you're into that stuff. If not, then just: it's pretty cool)

Edit: oh, you mean in the readme?

[00dani]

I'm not sure I like the name fromNodeCallback. True, Node callbacks do use the (err, res) format, but they're not the only ones who ever do that.

Perhaps call it fromErrCallback, to be more general?

[abesto]

@00Davo I'd prefer to call it fromNodeStyleCallback, but maybe that's a bit too long. You're right in that Node.js is not the only place where we see callbacks like this, but I've often seen it referred to as "node-style callback". Even if it wasn't introduced by node, it's certanly become a standard due to the popularity of node.

To me, the fromErrCallback name means that the method takes several callbacks, one of which is an error callback, and we're creating a stream from that.

Bottom line: I still prefer fromNodeCallback, but I won't take it personally if we go with another name.

[raimohanska]

I guess "node-style callbacks" are well-known enough to warrant for the name fromNodeCallback.

The example code is pretty cool and I also like the fact that you only need to deal with errors in a single spot. And yes, I'm a kind-of-a Haskellist too, having written reactive-bacon before starting to work on bacon.js.

I hope you don't mind if I do some code review for you. The code looks very good, but some simplifications could probably be made. Looking at the update function, you could use Bacon.constant to create a constant Property, instead of Bacon.once. So, on line 46, you could write

var key = Bacon.constant(tabKey(req.params.id))

Now because key is really just a constant value, you could still simplyfy to

var key = tabKey(req.params.id)
var json = Bacon.redis('get')(key)

Also, on the last line, you have

Bacon.combineWith([obj, update], fst).respond(res);

While you could have instead just

update.respond(res);

Right?

Oh, and you can use plain flatMap instead of flatMapLatest in most cases. Probably all cases in this file.

The bottom line is, I'm pretty convinced we should include fromNodeCallback. Could you come up with a simple example that could be included in the README?

[abesto]

Wow, thanks for the suggestions :) You're right on all counts. I guess bacon.js is such a shiny hammer, even constants look like nails.

I've added two simple examples (with and without error), using the example for fromCallback to keep things simple. How do you like it?

[raimohanska]

Yeah, it's quite a hammer :) I recently bought a Fein Multimaster and been trying to fit it to all kinds of jobs I've done just fine without the new tool.

Actually I was thinking of more realistic examples, involving some real Node.js APIs. That would also serve to demonstrate the partial application capabilities.

[abesto]

How about this? Uses a real node.js api, shows partial application and error handling, and still quite simple to understand.

[raimohanska]

That's it! Merging.

A blog post on server-side Bacon would be nice too. It would be nice to demonstrate how you can avoid the infamous callback hell, while taking care of error handling in a reliable and simple way. The problem is that I haven't done any serious node dev for some time and feel a bit lacking in credibility there, like "if I did node dev, this is how I'd do it".. Well, I should probably do my next server in node+bacon.

[abesto]

I'm planning to rewrite the whole shoppinglist thing with bacon. I'll probably write a post about what I learned in the process, thanks for the idea! (and the merge :))

[00dani]

I'm happy with the name fromNodeCallback given the understanding that it's short for Node-style callback. ^_^

I'd also very much like to see an example of Bacon.js being applied on server-side with Node, so that'd be good.

[kristianmandrup]

Hi,

I'm trying to use BaconJS for the first time for the following use case:

for (model in models) {
  store.subscribe(model, function(err, data) {
  });
}

Looking at http://abesto.net/bacon-js-on-the-server/ and http://howtonode.org/node-redis-fun

r.incr( 'nextid' , function( err, id ) {

id = Bacon.fromNodeCallback(redis.incr, 'tab').toProperty()

So the above would be:

var subscribed = {};
for (model in models) {
  subscribed[model] = Bacon.fromNodeCallback(store.subscribe, model).toProperty();
}

do some flatMap on properties?

[raimohanska]

Your code above creates a hash of Properties. What are you trying to achieve? Also, Issues are not really a support forum. I suggest you use Stack Overflow, which is better for sharing problems/solutions.