whatwg/tc39/node.js JSON modules

[dnalborczyk]

Bug report Change request

(this is not exactly a bug), more a change in behavior request to align with other implementations.

the expected change would be to be consistent with (see below) whatwg/tc39/node.js and treat a json module import as a default import, and do not allow or support named exports.

basically throw a warning, same or similar to what v4 does with js modules not having a named export, e.g.

WARNING in ./src/index.js 3:12-16
"export 'test' was not found in './data.json'

couple reasons for not considering named exports: confusing and non-consistent behavior of "JSON Object" vs "JSON Array" (+ others, "string", null etc.). Also how to handle a "default" property on an "JSON Object".

additional background:

WHATWG
whatwg/html#4315
https://html.spec.whatwg.org/#json-module-script
https://html.spec.whatwg.org/#creating-a-json-module-script (give it some time to load)

TC39 https://docs.google.com/presentation/d/1w8jWjD41htD7VxOejFqiHi6uGgHVWtZ_XmgFxgKkS7Q/edit#slide=id.g5947c7781f_0_20

Node.js modules working group
nodejs/node#27752

related Rollup issue:
rollup/rollup#2920

** Expected Behavior

// allow
import data from './data.json'

// disallow
import { foo } from './data.json'

this would be a great addition for v5, as it would be a breaking change. not sure about the feasibility of integrating the same in v4 since it's only a warning.

edit: added Rollup issue reference

[dnalborczyk]

awesome! thanks @sokra !

[dnalborczyk]

@sokra some additional information regarding JSON module imports:

the above mentioned [previous] proposal has been changed to: https://github.com/tc39/proposal-json-modules (currently stage 2), which was spun off from: https://github.com/tc39/proposal-import-assertions/ (stage 3)

allowing only the default import for JSON modules still stands, although the import will use an additional import assertion. I believe importing JSON without the assertion would not be allowed.

[sokra]

Nevertheless, the interpretation of module loads with no assertions remains host/implementation-defined, so it is valid to implement JSON modules without requiring assert { type: "json" }. It's just that assert { type: "json" } must be supported everywhere. For example, it will be up to Node.js, not TC39, to decide whether import assertions are required or optional for JSON modules.

Current it's optional. We will support the assert syntax once we can parse it (acorn)

[ljharb]

Importing JSON without the assertion is explicitly allowed, and imo encouraged.