W3C home > Mailing lists > Public > www-style@w3.org > February 2013

Re: [cssom] Proposal for obtaining robust style information via Javascript - getStyle()

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Thu, 31 Jan 2013 21:35:42 -0500
Message-ID: <510B29FE.7030107@mit.edu>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
CC: www-style list <www-style@w3.org>
On 1/31/13 9:23 PM, Tab Atkins Jr. wrote:
> Wait, getComputedStyle is a live object?

Yes.  And yes, that makes it an incredible pain to implement.

> Nah, let's just return a dead object.  It's for when you do need to request multiple
> properties, without having to retype the function multiple times (or
> get the UA to recompute things multiple times, if it can save effort
> by combining things).

There's a good chance that returning a dead object, which must therefore 
have computed values for all the properties, will take more time than 
computing 2 or 3 property values even if you have to duplicate some 
work...  A quick glance in Gecko suggests that we currently support 
about 300 properties, not counting shorthands.  And I would expect that 
number to grow significantly if the current pattern of css3/4 modules 
breaking up existing properties into 4-5 shorthands continues.

Maybe UAs can internally optimize by returning an object which can 
produce dead values of properties on demand but doesn't actually compute 
them until asked...  Gecko can sort of do that maybe, at times, kinda 
(yes, lots of caveats).  Can't speak for others.

In any case, seems like this use case argues for being able to not pass 
a property name but still pass in a value type and pseudo-element, 
right?  That does argue for using a dictionary for the argument...

-Boris
Received on Friday, 1 February 2013 02:36:10 GMT

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