Gatsby Link: Perform high-priority prefetch on touchstart

[sebashine-branly]

Hey everyone,

By browsing https://github.com/gatsbyjs/gatsby/discussions?discussions_q=is%3Aopen+prefetch, there are lots of good ideas and suggestions that I don't want to paraphrase here but are worth a read.
My understanding of gatsby-link (based on the awesome documentation and by reading some discussions/issues and the source code) is that it allows pre-fetching of links on two levels.

I'll over-simplify here by pretending touch events are for mobile whereas mouse events are on desktop. I will stand corrected if this simplification is too much.

Priority	Desktop	Mobile	___loader call
low	Intersection Observer API	Intersection Observer API	enqueue
high	onmouseenter	none	hovering

Additionally, Gatsby Browser API contains disableCorePrefetching which seems to disable the low prefetch, but does not affect the high prefetch.

Piggybacking on this comment, I think that the exact same code from https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-link/src/index.js for onMouseEnter could be applied to onTouchStart. In other words, it should listen to touchstart events and call ___loader.hovering.

There are two advantages:

• without disableCorePrefetching, the users on touch-only devices now have a high-priority prefetch happening as well
• with disableCorePrefetching, the users on touch-only devices have a high-priority prefetch happening at the time the user showed a strong intent of navigating to a client-side link

In short, this feature request is about offering consistency for touch-only devices, compared to users with a device handling mouse events.

I am looking forward to hearing your opinion.