Support resolve hook

[zhoukekestar]

Support resolve hook. For #143

[guybedford]

Thanks for working on this. Is there a specific reason you're looking to implement an async hook or would a sync one also work? That could also simplify the implementation in folding it into the current resolver function.

[zhoukekestar]

My first version is just a sync function too. But if we want some dynamic components, maybe we need to fetch its dependencies asynchronously & lazily.

For example: we want to render a WebComponent but have no dependencies (and import map) when the page loaded. Trigger ( iframe page or something ) and render this WebComponent (Dialog) lazily when we need it may be our expectation.

Maybe it's not the best practice. But someone may need this feature in the future. 😀

[guybedford]

Yeah I'm open to either. But either way I would still rather fold the resolver hook into a single call in a single resolve function.

[zhoukekestar]

Then how about the API parameter defaultResolver in esmsInitOptions.resolve(id, parentUrl, defaultResolver);?
or Just scope the defaultResolver inside the resolveHook like:

async function resolveHook(id, parentUrl) {
  function defaultResolver(id, parentUrl) {}

  if ...
}

[zhoukekestar]

Just updated the PR, simplify the resolve hook.

[guybedford]

Thanks for your work on this. Still not quite there though, see the feedback further.

[guybedford]

The approach looks good, thanks for the work on this. See the last point about the nature of the defaultResolve function passed.

[guybedford]

Looks great, think we've cracked it.

Re the sync / async thing this also relates to what browsers will expose via import.meta.resolve. See eg whatwg/html#3871 for discussion. Chrome currently wants to implement a sync resolver I believe. If we permit an async resolver we may be constrained in future if import.meta.resolve turns out to go sync. But we can just make a breaking change in this project too I suppose.

[guybedford]

The last thing before landing this would be to include the README / documentation change.

[guybedford]

Rather than having a separate test-resolve-hook, can we just add this to the main suite in test/test.html? That will ensure it's captured by CI.

[guybedford]

Landed in 1301af1, test refactoring and Firefox 60 fixes in c6ee672.

[zhoukekestar]

Thanks, 🎉