Link rel=modulepreload synchronously fires load event if script exists in module map

[domfarolino]

What is the issue with the HTML Standard?

Per spec, if a <link rel=modulepreload as=script> becomes browsing-context connected, its special fetch and process the linked resource steps are run, which synchronously invoke fetch a modulepreload module script graph with a set of onComplete steps that simply fire a load or error event. This algorithm delegates to fetch a single module script, whose step 6 is:

If moduleMap[(url, moduleType)] exists, run onComplete given moduleMap[(url, moduleType)], and return.

This appears to be able to synchronously invoke script during insertion, which we generally see as a bad thing (i.e., mutation events). Rather, the firing of the load event should probably be done behind a queued task, as we do for error events in the error case.

[domfarolino]

Ugh, OK I've been bested by another usage of inline task queueing without nested steps. Turns out https://html.spec.whatwg.org/multipage/webappapis.html#fetch-a-single-module-script:~:text=If%20moduleMap%5B(url%2C%20moduleType)%5D%20is%20%22fetching%22%2C%20wait%20in%20parallel%20until%20that%20entry%27s%20value%20changes%2C%20then%20queue%20a%20task%20on%20the%20networking%20task%20source%20to%20proceed%20with%20running%20the%20following%20steps already queues a task to "proceed with running the following steps", and the step I point out in the OP above is in that set of queued steps. So I don't think any action needs to be taken here.