[Webkit-unassigned] [Bug 181905] New: CSS @supports feature detection

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Sat Jan 20 02:26:27 PST 2018


https://bugs.webkit.org/show_bug.cgi?id=181905

            Bug ID: 181905
           Summary: CSS @supports feature detection
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: All
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: nikhil.webkit at dezinezync.com

The CSS "@supports" syntax is useful for feature detection and progressive enhancements.

The following CSS code fails in 
- Safari 11.0.2 on macOS 10.12.6
- Safari Technology Preview Release 46 on macOS 10.12.6
- Mobile Safari on iOS 11.2.2

> @supports (-webkit-backdrop-filter: blur) {
>     #myElem {
>         -webkit-backdrop-filter: blur(10px);
>     }
> }

The associated JS for the above also fails:
> CSS.supports('-webkit-backdrop-filter', 'blur') || CSS.supports("backdrop-filter:blur") || CSS.supports("-webkit-backdrop-filter:blur")

Expected: The above is expected to return `true` and/or the CSS @supports block should be invoked.

Actual Result: 
1. The above JS code returns `false` and therefore disables the progressive enhancement path and the implementation requires checking the UA String for feature detection. 
2. The CSS @supports block is never parsed since feature detection fails although supported by the browsers.

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