Bacon example does not run as suggested

[Cefn Hoile]

I copied the code from an example describing how groupBy works, as I was suspicious that the operation on the stream in limitF actually did nothing.

In the limitF call, is a call to takeUntil, but the return value is never used, and no return value is passed back from the function. If I understand Bacon correctly, then the original stream is unchanged by the filter calls, and if the result is not used, so I'd expect there to be no side-effects. I was trying to run the example to investigate what was wrong with my mental model.

However, when I run the example against the current git distribution, it actually fails with a different error as follows.

require("./groupby.js");
{}
> 
/home/user/Documents/code/imagination/git/bacon.js/dist/Bacon.js:1246
        throw e;
              ^
TypeError: Cannot call method 'withHandler' of undefined
    at /home/cefn/Documents/code/imagination/git/bacon.js/dist/Bacon.js:2862:33
    at Next.valueF (/home/cefn/Documents/code/imagination/git/bacon.js/dist/Bacon.js:882:18)
    at Next.value (/home/cefn/Documents/code/imagination/git/bacon.js/dist/Bacon.js:871:35)
    at spawn (/home/cefn/Documents/code/imagination/git/bacon.js/dist/Bacon.js:2223:40)
    at Object.sink (/home/cefn/Documents/code/imagination/git/bacon.js/dist/Bacon.js:2274:22)
    at Dispatcher.pushToSubscriptions (/home/cefn/Documents/code/imagination/git/bacon.js/dist/Bacon.js:1236:23)
    at Dispatcher.pushIt (/home/cefn/Documents/code/imagination/git/bacon.js/dist/Bacon.js:1259:14)
    at Object.Bacon.UpdateBarrier.inTransaction (/home/cefn/Documents/code/imagination/git/bacon.js/dist/Bacon.js:350:18)
    at Dispatcher.push (/home/cefn/Documents/code/imagination/git/bacon.js/dist/Bacon.js:1227:28)
    at Dispatcher._handleEvent (/home/cefn/Documents/code/imagination/git/bacon.js/dist/Bacon.js:2824:23)

The original code (with the modification of the require call) is as follows...

var Bacon = require("baconjs");

var events = [
  {id: 1, type: "add", val: 3 },
  {id: 2, type: "add", val: -1 },
  {id: 1, type: "add", val: 2 },
  {id: 2, type: "cancel"},
  {id: 3, type: "add", val: 2 },
  {id: 3, type: "cancel"},
  {id: 1, type: "add", val: 1 },
  {id: 1, type: "add", val: 2 },
  {id: 1, type: "cancel"}
]

function keyF(event) {
  return event.id
}

function limitF(groupedStream, groupStartingEvent) {
  var cancel = groupedStream.filter(function(x) { return x.type === "cancel"}).take(1)
  var adds = groupedStream.filter(function(x) { return x.type === "add" })
  adds.takeUntil(cancel).map(".val")
}

Bacon.sequentially(2, events)
  .groupBy(keyF, limitF)
  .flatMap(function(groupedStream) {
    return groupedStream.fold(0, function(acc, x) { return acc + x })
  })
  .onValue(function(sum) {
    console.log(sum)
    // returns [-1, 2, 8] in an order
  })

...and it can be found under the heading "Calculator for grouped consecutive values until group is cancelled" at https://github.com/baconjs/bacon.js/

Is there something I'm doing wrong which means this example doesn't work.

[Juha Paananen]

There's a return missing from the limitF function above.

[Juha Paananen]

I fixed the example in the readme.