How are the module attributes interpreted across host environments? · Issue #10 · tc39/proposal-import-attributes (original) (raw)

Note: The module attributes proposal would not require or recommend that hosts use any particular interpretation of the attributes. Some people in the JS community have a goal of non-Web environments working towards partial Web-compatibility, but such efforts lie outside of the scope of this proposal. This issue exists for brainstorming and requirements gathering that may feed back into the module attributes proposal, but not to make any sort of requirement or recommendation for JS environments.

The ECMAScript specification leaves resolution of module specifiers up to the host environment, e.g., HTML or Node.js. Probably we'd do the same for this proposal. At the same time, there's a broad effort to define similar semantics across many embedding environments. For one example, JSON modules make just as much sense in HTML and Node.js, even if they would have some host-specific semantics (e.g., checking the MIME type on the web). How should we coordinate to build compatibility here?

I want to suggest that, specifically for module types, we could have the logic to dispatch on certain type strings (initially, just JSON) and give them semantics in ECMA-262, or say "no interpretation" and fall back to the host. This would be invoked after the MIME type is checked. There's more details to work out when writing the spec to verify that it's a viable layering, though.

(Edit: Added the following paragraph to replace the previous one)

I want to suggest that the host be responsible for handling module attributes, and may use facilities provided by ECMA-262 to handle certain module types, for example JSON modules. It's still to be determined whether non-Web hosts would want to require a type: declaration the way it seems like the Web would.

Would non-web hosts still require with type: "json", or would they be comfortable relying on the file extension? Would tooling end up adding with type: "json"? My personal preference at this point is to require the author to include this in all cases, for maximum consistency/compatibility across environments, but this is a tradeoff for ergonomics and incremental upgrade. I'd be interested in hearing your thoughts.