Disallowing unused values

[jugglinmike]

As far as I know, the following construction, though syntactically valid, would never be used intentionally since ParseJSONModule has no side effects:

import 'data.json' assert { type: 'json' };

In that case, disallowing it could surface programming errors. I'm not sure if the restriction would justify the complexity of another early error, though. Is it better left to linters?

[jugglinmike]

One the other hand, an early error like this could become a source of inconsistency. Hosts won't be able to apply it to their own import assertions even in cases where the same rationale (that is: "there is no side-effect") applies.

[ljharb]

It would have an effect, though - which is to fail the module graph if the JSON is invalid, and to populate the cache (thus, disallowing it would be preventing code that does have a use case).