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Re: [ACTION-59] Introduce lookup by id structures for streams and tracks.

From: Stefan Hakansson LK <stefan.lk.hakansson@ericsson.com>
Date: Tue, 6 Nov 2012 14:18:16 +0100
Message-ID: <50990E18.2090505@ericsson.com>
To: public-webrtc@w3.org
On 11/05/2012 02:36 PM, Adam Bergkvist wrote:
> ACTION-59 is about moving away from a model where index is the only way
> to look up streams and tracks in
> PeerConnection.localStreams/remoteStreams and
> MediaStream.audioTracks/videoTracks.
> I see two common cases how these stream and track collections will be used.
> 1) Lookup by id.
> 2) Iterate/loop through all the items in the collection.
> Item 1) is easily solved by a getStreamById()/getTrackById() method.
> Item 2) could be achieved in a few ways and I would like to get some
> feedback on which way people in group prefer.
> I don't think the "for (var p in collection)"-approach is something we
> want to use here. It won't give us the result we want since it includes
> additional properties added with a "collection.someProp = ..."
> assignment as well as inherited constants, methods and attributes.
> Here are two options on how to solve item 2) (iteration) from the list
> above. I you have a better approach, feel free to suggest it.
> A) forEachStream()/forEachTrack() method
> You iterate through all the items by providing a callback to the
> forEachStream() method. The callback will be called synchronously for
> each item.
> Example:
> pc.localStreams.forEachStream(function (stream) {
>      // use stream
> });
> We could have the callback return a boolean value which could be used to
> "break" the iteration if the desired item was found before the end was
> reached.
> B) Keep the possibility to use indices for looping (but not guarantee
> the order)
> This kind of looping may be more familiar to developers, but it exposes
> the index that may be problematic if used outside of the "looping
> context". The reason for proposing this as an alternative is that the
> video element does this for its track lists.
> Example:
> for (var i = 0; i < pc.localStreams.length; i++) {
>      // use pc.localStreams[i]
> }
> What do people think?

Honestly I have no strong preference. Both seem to work fine, and 
preserve the structure MediaStream -> MediaStreamTrackList -> 
MediaStreamTrack (which I have not seen strong arguments for changing so 

But "forEach" seems safer as it does not invite to mistakes from the app 
developer, so my vote goes for that option.


> /Adam
Received on Tuesday, 6 November 2012 13:18:45 UTC

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