Add support for <link rel=preload>

• Component: Page Loading
• Status: RESOLVED FIXED

[sideshowbarker]

Preload provides a declarative fetch primitive that initiates an early, high-priority, and non-render-blocking fetch and separates fetching from resource execution.
Declaratively specifies which resources (e.g., fonts) the user agent must fetch early to improve page performance.

- spec: https://w3c.github.io/preload/
- use cases: https://w3c.github.io/preload/#use-cases

Browser-engine support:

- Blink: Shipped in Chrome 50 https://developers.google.com/web/updates/2016/03/link-rel-preload?hl=en
- Edge: “Priority: Medium — Development is likely for a future release” https://developer.microsoft.com/en-us/microsoft-edge/platform/status/preload
- Gecko: Open feature bug https://bugzilla.mozilla.org/show_bug.cgi?id=1222633

[Yoav Weiss]

I'm currently implementing this feature (but failing to assign this issue to myself *shrug*).

Related bugs:
https://bugs.webkit.org/show_bug.cgi?id=156334 - initial preload support
https://bugs.webkit.org/show_bug.cgi?id=157988 - Preload single download tests.
https://bugs.webkit.org/show_bug.cgi?id=156773 - LayoutTest http/tests/preload/dynamic_remove_preload_href.html is flaky on Mac and iOS

[Yoav Weiss]

Also related: https://bugs.webkit.org/show_bug.cgi?id=158466

[Domenic Denicola]

Please note the tests at http://w3c-test.org/html/dom/reflection-metadata.html for link.as.

[Jake Archibald]

I imagine it's in-progress, but neither fetch() or XHR appear to use the preload cache in the latest technology preview.

[Addy Osmani]

Hey Yoav. Are there other blocking bugs to complete the link rel=preload implementation atm? Just came across https://bugs.webkit.org/show_bug.cgi?id=161952 but you might be keeping track of others.

[Yoav Weiss]

No, just lost track of this issue :)

I think we can close this meta-bug and open new ones for eventual issues.