Auto-sizes for lazy-loaded images in HTML

[marcoscaceres]

Request for position on an emerging web specification

(Please delete inapplicable rows.)

• WebKittens who can provide input:

Information about the spec

• Spec Title: Add sizes=auto to lazy-loaded <img>
• Spec URL: Add sizes=auto to lazy-loaded <img> whatwg/html#8008
• GitHub repository:
• Issue Tracker (if not the repository's issue tracker): Add "auto sizes" for lazy-loaded images whatwg/html#4654
• Explainer (if not README.md in the repository):

Design reviews and vendor positions

• TAG Design Review:
• Mozilla standards-positions issue: Auto-sizes for lazy-loaded images in HTML mozilla/standards-positions#650

Bugs tracking this feature

• WebKit Bugzilla: https://bugs.webkit.org/show_bug.cgi?id=253143
• Radar: rdar://106416138

Anything else we need to know

On webkit-dev, @zcorpan wrote:

I'd like WebKit's position on the proposal: Add sizes=auto to lazy-loaded <img>

This allows web developers to omit the sizes attribute, or explicitly specify sizes=auto, for <img> elements that have loading=lazy. The browser will use the layout width of the image as input to the srcset resource selection (lazy images don't start loading until layout is known, at the earliest). For eager-loading images, it's invalid and equivalent to 100vw.

Chromium position:
whatwg/html#4654 (comment)

[hober]

@smfr @rniwa @litherum @jensimmons, thoughts?

[annevk]

Colleagues and I think this is a reasonable addition. I suggest we mark this as "position: support" in seven days.

[hober]

Closing as we've identified our position.