JavaScript API general discussion

[domenic]

What is document.loadingMode? All we see is its type property, right?

Should we use a promise instead of the sync getter + change event pattern?

[jeremyroman]

This is a bit of an attribute of the generality. I think that the simpler use cases are probably best served by something like privacycg/storage-access#55, which is simply a promise.

My thinking here was to expressly expose what the current loading mode is, which matters more if this expands. For example, if we end up needing "network-isolated" and "fenced" as separate modes, you'd want to be able to distinguish them. And some of these might make sense to parameterize (for example, we might wish to expose the notion of being proxied in some way), so exposing a dictionary or interface rather than an enum makes this more extensible.

If we're going to have an underlying primitive of "you are in this loading mode [therefore permissions policy is restricted in these ways, therefore you shouldn't necessarily record an impression, therefore ...]" in the spec, it seems natural to me to expose that to the platform too.

[domenic]

Summarizing some discussion from #5 (comment) :

We have a few paths we could go with a JS API for prerendering and other loading modes.

• Super-minimal; no dedicated API. Maybe add a "prerender" mode to visibilityState, since per @bokan that seems web-compatible. (And it already has a change event.) But mostly people rely on purpose-specific APIs like permissions and storage access.

• Minimal but extensible. That's what the current proposal, slightly modified by First draft of prerendering browsing context #5, is trying to do. It has a LoadingMode interface, which so far only has EventTarget / onchange and the type property, but could grow if we want it to. The main delta vs. super-minimal here is that it allows distinguishing things like prerender vs. uncredentialed-prerender directly, instead of relying on other APIs like hasStorageAccess().

• Maximal, i.e. expose a bunch of useful data. (But, we don't know exactly what that is yet.)