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Re: [battery] Should getBattery() always return the same promise?

From: Rick Waldron <waldron.rick@gmail.com>
Date: Tue, 1 Jul 2014 17:15:29 -0400
Message-ID: <CAHfnhfrgg5Gy6bdDx-EZskUFrA5r4fvh8=8TcRyRq3UHb5K+sw@mail.gmail.com>
To: Mounir Lamouri <mounir@lamouri.fr>
Cc: public-device-apis <public-device-apis@w3.org>, Domenic Denicola <domenic@domenicdenicola.com>
On Tue, Jul 1, 2014 at 6:03 AM, Mounir Lamouri <mounir@lamouri.fr> wrote:

> Hi,
>
> When I wrote the getBattery() prose, I made it so that getBattery()
> would return a new promise every time it is called but it would always
> return the same BatteryManager when the promise is resolved.
>
> I realised that this requirement probably doesn't make much sense and we
> might want to spec getBattery() as returning always the same promise. In
> other words, navigator.getBattery() === navigator.getBattery(). The
> intent isn't really to get the equality but that way, we simplify the
> implementation because implementing this only require to keep track of
> that one promise.
>


Is there a design history document or thread that explains the reasoning
that lead to an API that returns a promise here? The battery exists before
the browser ever loads a site and its JavaScript files, so why does
`getBattery` need to be a promise? The "latest published" Battery Status
API spec makes more sense: navigator.battery is always a single instance of
BatteryManager that exists as specified here:
http://www.w3.org/TR/battery-status/#navigatorbattery-interface . Why does
it need to be "requested" via a "getBattery" API that itself doesn't return
a BatteryManager object, but promises to produce one (and always the same
one)?

If it's always the same BatteryManager instance, it's not clear how this
API usage:

navigator.getBattery().then(function(battery) {
  battery.onlevelchange = function() {
    console.log("level changed!");
  };
});


... is at all superior to this:

navigator.battery.onlevelchange = function() {
    console.log("level changed!");
});


Even if the argument is that not all code needs or wants to allocate the
BatteryManager, then the solution is simply to make `navigator.battery` an
accessor to the BatteryManager instance.


Rick
Received on Tuesday, 1 July 2014 21:16:18 UTC

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