[whatwg] [canvas] Proposal for supportsContext

[Tobie Langel]

On Tue, Sep 11, 2012 at 10:34 AM, Simon Pieters <simonp at opera.com> wrote:
> On Tue, 11 Sep 2012 00:14:25 +0200, Glenn Maynard <glenn at zewt.org> wrote:
>> If you really want to protect users from the behavior of pages, you'd
>> really need to make creating the context cheap.
>
> This was exactly my reaction as well. Introducing a new method doesn't solve
> the problem. There will still be pages that create the context and then
> don't use it. Browsers just have to suck it up and be fast anyway, just like
> with all other features on the Web.
>
> I think we shouldn't add supportsContext() since it doesn't provide authors
> with new information and browsers will have to do the above anyway.

I actually like Ashley Gullen's proposal (canPlayType-inspired)
because it brings consistency to the platform and offers a general
pattern on how to test for the presence of features which can't be
asserted for certain without costly lookups.

navigator.onLine property is another example where a similar pattern
would make (more) sense (than the current boolean returned instead).

Basically, this is trading performance for the risk of false positives.

--tobie