[whatwg] RWD Heaven: if browsers reported device capabilities in a request header (Boris Zbarsky)

Kornel Lesiński kornel at geekhood.net
Mon Feb 6 14:16:32 PST 2012

On Mon, 06 Feb 2012 20:00:45 -0000, Irakli Nadareishvili  
<irakli at gmail.com> wrote:

> 1. Adaptive images:
> To optimize user-experience on smart-phones (most of which have  
> relatively small screens, and are on slow connections most of the time)

Be careful with generalizations like that.

Mobile devices can be connected to high-speed networks. Laptops can be  
tethered via mobile networks.

There are many permutations of screen size, DPI, zoom, network speed,  
bandwidth cost and memory availability that influence decision what image  
resolution is best, and it's not as simple as "mobile" vs "non-mobile".

There aren't even clear "device classes". Basic device characteristics  
like physical screen size and presence of a hardware keyboard can change  

Smartphones can be connected to TVs and projectors. Tablets can be  
connected to keyboards. Laptops can be flipped into tablet mode. Desktops  
can have touchscreens — and these aren't obscure things. It's iPad with  
AirPlay and dock. It's most tablet PCs. You can expect many laptops to  
have touchscreens soon.

"Mobile" or "smartphone" can mean anything from Opera Mini on GPRS  
connection to a quad-core 4G smartphones more powerful than desktops were  
few years ago.

I appreciate optimisations you're trying to make, but simply reporting  
basic capabilities in an HTTP header isn't going to work well in other  
than few most common cases.

I hope we could come up with a better solution that can all the  
optimisations and improved experience you want to achieve, but doesn't  
have pitfalls of assuming that slow networks and touch screens go  
hand-in-hand, or that devices with keyboards also have mouse and < 100dpi  
screen, etc.

> 2. Adaptive CSS/Javascript.

CSS has media queries already. New queries can (and I think should) be  
added to query more capabilities like presence of a touch screen (Mozilla  
experiments with -moz-touch-enabled media query already).

Media queries are dynamic and can be observed by JavaScript, so when you  
switch from tablet's own touch screen to an external display, pages could  
theoretically switch UI too.

> If server could easily detect device type/capabilities it would have the  
> ability to tailor aggregated js/css files to a class of a device, thus  
> providing greatly improved experience.

Sure, but it doesn't mean that the server has to do that and that it's the  
only way to do that. For example:

<script src=touch-ui.js media="input-type: touch">
<script src=mouse-ui.js media="input-type: mouse">

(although I'm not suggesting using that form literally, as it has some  
drawbacks of its own)

Next version of JavaScript is going to have modules, which makes loading  
of JavaScript cleaner than <script>. Perhaps modules could be loaded  
conditionally based on media-query-like declarations?

regards, Kornel Lesiński

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