[whatwg] Challenging canvas.supportsContext

[Brandon Benvie]

On 6/19/2013 2:05 PM, James Robinson wrote:
> What would a page using Modernizr (or other library) to feature detect 
> WebGL do if the supportsContext('webgl') call succeeds but the later 
> getContext('webgl') call fails?

I don't have an example, I was just explaining how Mozernizr is often used.

> I'm also failing to see the utility of the supportsContext() call. 
>  It's impossible for a browser to promise that 
> supportsContext('webgl') implies that getContext('webgl') will succeed 
> without doing all of the expensive work, so any correctly authored 
> page will have to handle a getContext('webgl') failure anyway.

Given this, it would seem supportsContext is completely useless. The 
whole purpose of a feature detection check is to detect if a feature 
actually works or not. Accuracy is more important than cost.