code-splitting: incorrect handling of import modules as not found when encountering temporary error

[prasannavl]

When a module is imported say with import("x") -- If the import fails due to a network failure. Parcel permanently seems to throw the same error that was received (in this case ERR_INTERNET_DISCONNECTED and reports module as MODULE_NOT_FOUND. This is incorrect. Parcel should always discard module load errors, so any fresh request can succeed.

PS: Webpack handles it correctly as described as well.

[await-ovo]

I'd like to fix this issue, and in my opinion just delete bundles[bundle]= can send fresh request, but i don't know if this will cause side effects . could someone help me?

[DeMoorJasper]

@diem98 not sure that's a good idea. As bundles[bundle] prevents loading bundles more than once (which is quite important if you'd load it in 20 diff places at the same time), and as far as I know it also contains the bundle, which isn't just true as you did.
Perhaps you could catch the error and do delete bundles[bundle] in that catch clause (and possible try to load the bundle again after a couple 100 ms?)

[await-ovo]

Thanks for your detailed explaining, but i wonder if we really need retry load bundle. if do the retry, then should try how many times or just one time? I think maybe just throw error as expected will enough.:)

[DeMoorJasper]

@diem98 What about changing the code to this:

if (bundleLoader) {
  return bundles[bundle] = bundleLoader(getBundleURL() + bundle)
    .then(function (resolved) {
      if (resolved) {
        module.bundle.register(id, resolved);
      }
 
      return resolved;
    })
    .catch(function (e) {
      delete bundles[bundle];
      // re-throw to be caught by the user
      throw e;
    });
}

*Haven't tested the code yet, so it's just an idea

and leaving the retry behaviour as future work?

[prasannavl]

@DeMoorJasper that looks good. However, I think it would be nicer to throw a custom error type, so that it can be caught specifically and handled by user code, for network failure.

And I don't see why retry has to be a part of this at all. The user code can always do the import that failed again if needed. I think retry introduces unnecessary magic and causes more problems than it solves. Without it, it's simple and deterministic - Either fails, or succeeds. Failure with a proper error type can be caught in user code and retried depending on the need of the application. (which is also consistent with webpack behavior).

[DeMoorJasper]

@prasannavl alright sounds good, I've opened up a PR would be great if you could test it out to see if it does what you expect it to do.