Speculation rules: mobile "eager" eagerness improvements

Category: Performance
Type: No developer-visible change
Status: Proposed (Chrome Proposed)
Intent stage: None

Summary

On mobile, "eager" eagerness speculation rules prefetches and prerenders now trigger when HTML anchor elements are in the viewport for a short time. The previous behavior, of starting prefetch/prerenders as soon as possible, was the same as "immediate" eagerness. This new behavior is more useful as it better reflects the author's intent to be more eager than the "moderate" and less eager than "immediate". More detail on this and other upcoming improvements to speculation rules eagerness are available at https://docs.google.com/document/d/1YPbtUPfZIDElzBZNx8IQMzRFvy8oauLG_i1XIr6jgTs/edit?usp=sharing.

Standards & signals

Specification: https://html.spec.whatwg.org/multipage/speculative-loading.html#speculative-loading
Firefox: Neutral — We have not asked Firefox for their thoughts on this specific change. They are positive on and implementing prefetching, and will likely make their own choices for how to implement each eagerness level.
Safari: No signal — We've not asked Safari for their thoughts on this specific change. They have recently indicated a tentative positive position towards conservative-eagerness prefetching.
Web developers: Positive — We've seen several developers re-create this viewport-based technique using JavaScript to manually insert and remove speculation rules, e.g. in the Quicklink library.
Tracking bug: https://crbug.com/436705485

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