[whatwg] Challenging canvas.supportsContext
simonp at opera.com
Tue Jun 25 13:28:08 PDT 2013
On Tue, 25 Jun 2013 21:01:27 +0200, Dean Jackson <dino at apple.com> wrote:
> Showing or hiding interface objects is not something I want to do.
It's possible that I missed it, but, why not? There is precedent for doing
so. For instance, in Opera 11, the WebSocket constructor was absent unless
WebSockets were enabled in opera:config. This allowed feature detection
like the following to work:
var supports_websockets = "WebSocket" in window;
Also, the HTML spec actually requires it:
When support for a feature is disabled (e.g. as an emergency measure to
mitigate a security problem, or to aid in development, or for performance
reasons), user agents must act as if they had no support for the feature
whatsoever, and as if the feature was not mentioned in this specification.
For example, if a particular feature is accessed via an attribute in a Web
IDL interface, the attribute itself would be omitted from the objects that
implement that interface — leaving the attribute on the object but making
it return null or throw an exception is insufficient.
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