Suggestion: Add more fine-grained prioritization for prefetching

[cjtenny]

The example in subresource-loading.md has the following manifest:

    "paths": {
        "a.js": ["bGpobG", "FzZGZq"],
        "b.js": ["bGpobG", "sbnNkd"],
        "style/page.css": ["a2FzaG"],
    }

(implicit: common.js => bGpobG)

However, there's no way to indicate whether a resource is needed immediately or soon here, which would help in batching requests and with page responsiveness. For example, a.js and b.js might depend on common.js to be able to execute, but may also insert loading-wheel.gif into the page when running and be able to start executing / return control to the user before that soft dependency loaded. Similar to priority hints, a mechanism here & in the proposed bundle navigator control mechanism could offer larger sites much needed control to maintain responsiveness while using bundles.

[littledan]

I like this idea. I could imagine that the array could be generalized into a split between initial fetch vs separate prefetch at high/auto/low priority. I think this would fit in pretty cleanly into an extension on top of this proposal (e.g., we could make objects as array elements to specify these priorities, and in the v1, say that objects positioned this way are ignored). What would you think of this as a v2 feature? It's a bit hard to get into priorities before the priority hints proposal is standard, though.

[cjtenny]

I think possibly it points to something worth reviewing a little more in a v1 to see if it could be improved.

Thinking more about it, what are the reasons to have dependencies hard-coded in the manifest versus dynamically decided by the client or server? I think the dependency path list is trying to solve two separate problems in one go: batching less-than-full-bundle requests and allowing a CDN to serve bundles without needing to understand dependencies. Could there be a better way to combine those, or offer control separately?

[littledan]

Well, if you have any other ideas, I would be happy to hear them. The subresource loading section includes multiple schemes to consider, and I would be open to adding others.