Perhaps I should have been more clear. When I said streams are finite I
meant that you know when they are done. If you haven't gotten an "end"
event, you can expect more data in the future. Once there is an "end",
it's done. This is important for things like cross-process resource
management.
Isaac explained everything very well so I won't repeat it. :)
On Sat, Apr 28, 2012 at 4:51 PM, Glenn Block <glenn.bl...@gmail.com> wrote:
> OK so really what you are saying is if you feel more comfortable using
> callbacks no problem doing that, but event emitters are totally suitable
> for this.
>
> perf wise, is there a significant difference between the two approaches?
> How much do you pay for emitting an event over just invoking a callback or
> vice versa?
>
>
> On Sat, Apr 28, 2012 at 11:09 AM, Isaac Schlueter <i...@izs.me> wrote:
>
>> On Sat, Apr 28, 2012 at 10:42, Glenn Block <glenn.bl...@gmail.com> wrote:
>> > So given the case of a multi-step process where each step needs to be
>> > performed async you would recommend callbacks/named callbacks right?
>>
>> If each step is independent of each other step, then callbacks are fine.
>>
>> obj.doThing(function (er, ok) {
>> // ok, done now
>> obj.doAnotherThing(function (er, ok) {
>> // done with the other thing now
>> })
>> })
>>
>> is a bit more humane than:
>>
>> obj.doThing()
>> obj.once("didthing", function () {
>> obj.doAnotherThing()
>> obj.once("didanotherthing", function () {
>>
>>
>> That being said, the most common use case for event emitters in node
>> is when there's exactly one listener. That's why we optimize the hell
>> out of that case. It's perfectly fine to use them in cases where
>> there'll be one listener. The relevant difference is if the event
>> setup and the method call are separate from one another conceptually.
>>
>> A callback is "Do X and then when it's done, let me know". An event
>> is "Any time X happens, let me know", which may be triggered by some
>> other thing somewhere else in teh program doing something.
>>
>>
>> On Sat, Apr 28, 2012 at 11:02, Mark Volkmann <r.mark.volkm...@gmail.com>
>> wrote:
>> > On Sat, Apr 28, 2012 at 9:07 AM, Tim Caswell <t...@creationix.com>
>> wrote:
>> >> A stream is some query that emits a finite stream of data.
>> > So do we have agreement that if a stream never emits an "end" event
>> > then something went wrong and this is never intentional? Maybe this is
>> > one criteria for choosing between EventEmitter and streams. Choose
>> > EventEmitter when there is no guaranteed end of data.
>>
>> No. Streams are not necessarily finite. Consider the case where you
>> have a video camera streaming data. You might have a stream of mpeg
>> chunks or something, but it won't necessarily end (unless someone
>> shuts off the video camera.) Or even simpler, say you have a TCP
>> connection from one server to another. Under normal circumstances,
>> that connection might not be severed for days, or years, or longer.
>>
>> The finiteness of a Stream is determined by the thing it represents,
>> not by anything essential to the abstraction.
>>
>> Choose Streams when it is a stream of buffers and strings that you
>> need to be able to pause and resume, as in the case of TCP
>> backpressure.
>>
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