support import assertion

[wenerme]

Description of Proposed Feature

Same sematic of

import 'a'
import 'b' assert {type: 'css'}
import 'c'

await import('d', {assert:{type:'xyz'}})

In what way would you use it?

import

• pass one more args add register import meta placeholder #2433

System.register(
  ["a", 'b', "c"],
  () => void 0,
  [,{ assert: { type: "css" } } ,]
);

import()

• add dynamic import meta placeholder #2431

System.import('d',{assert:{type:'xyz'}})

---

• xref rollup [v3.0] Basic support for import assertions rollup/rollup#4646

[guybedford]

Would be great - Babel and TypeScript could also be updated to support this output when transpiling. I wonder how we would integrate it into the imports of the System.register format?

[wenerme]

What do you mean integrate it into the imports of the System.register format ? Dose #2433 solve the problem ?

[guybedford]

I guess the guidance needs to be put together for transpilers and tools primarily? Ie things like - should import assertions always be output? What format should they be output as? etc. You can PR https://github.com/systemjs/systemjs/blob/main/docs/system-register.md to update this guidance.

[ExE-Boss]

Note that the spec has now changed to import attributes and reuses the with keyword:

• Allow assertions to affect module loading, change keyword to with tc39/proposal-import-attributes#131
• Rename from "assertions" to "attributes" tc39/proposal-import-attributes#134