Is Deno's implementation of dynamic import() ECMA-262 and test262 conformant?

[guest271314]

Consider this code from here Deno dynamic import("./exports") throws module not found for "exports.js" dynamically created in the script.

Note: A workaround for this is to use import(import.meta.resolve("./exports.js")), though I don't think we should have to use specialized behaviour for dynamic import() for Deno.

Very simple question: Is Deno's implementation of dynamic import(), that throws when raw string specifier is used to dynamically import() a script created and written to the underlying file system within the running script ECMA-262 and test262 conformant?

// Deno dynamic import("./exports") throws module not found for "exports.js" dynamically created in the script
// dynamic_import_always_throws.js
// References: https://www.reddit.com/r/Deno/comments/18unb03/comment/kfsszsw/ https://github.com/denoland/deno/issues/20945
// Usage:
// deno run -A dynamic_import_always_throws.js
// bun run dynamic_import_always_throws.js
// node --experimental-default-type=module dynamic_import_always_throws.js
import { open, unlink } from "node:fs/promises";
const runtime = navigator.userAgent;
const encoder = new TextEncoder();
try {
  const script = `export default 1;`;
  // deno
  if (runtime.includes("Deno")) {
    await Deno.writeFile("exports.js", encoder.encode(script));
  }
  // node
  if (runtime.includes("Node")) {
    const dynamic = await open("./exports.js", "w");
    await dynamic.write(script);
    await dynamic.close();
  }
  // bun
  if (runtime.includes("Bun")) {
    await Bun.write("exports.js", encoder.encode(script));
  }
  const { default: module } = await import("./exports.js"); // Raw string specifier
  console.log({ module });
  console.log({ runtime });
} catch (e) {
  console.log("Deno always throws.");
  console.log({ runtime });
  console.trace();
  console.log(e.stack);
} finally {
  console.log("Finally");
  // node, bun
  if (runtime.includes("Node") || runtime.includes("Bun")) {
    await unlink("./exports.js");
  } // deno
  else if (runtime.includes("Deno")) {
    await Deno.remove("./exports.js");
  }
}

[bnoordhuis]

Very simple question: Is Deno's implementation of dynamic import(), that throws when raw string specifier is used to dynamically import() a script created and written to the underlying file system within the running script ECMA-262 and test262 conformant?

Yes. ECMA-262 doesn't demand anything from implementers. I can't link directly to the right clauses for some reason¹ but it's 13.3.10 Import Calls and then 16.2.1.8 HostLoadImportedModule:

The actual process performed is host-defined [..]

It's arguably a quality-of-implementation issue but not a spec conformance issue.

¹ the closest I can link to is https://tc39.es/ecma262/#sec-ecmascript-language-scripts-and-modules

[guest271314]

Pardon, had a system crash.

I am having a challenging time conceiving of a raw string specifier for dynamic import() test where Node.js, Bun, and every other JavaScript runtime that implements dynamic import() not throwing results in a PASS and Deno's implementation that does throw for raw string specifier where the script is created in the running script also results in PASS.

I can't think of any other interface or specification where that is the case.

[guest271314]

So, for example if that was a test in test262, how do you reconcile Deno's dynamic import() throwing for raw string specifier created in the running script throwing and every other JavaScript runtime not throwing for that case? How can a PASS be the result without special consideration for Deno?

[guest271314]

I guess this https://tc39.es/ecma262/#sec-HostLoadImportedModule does include the ambiguous term "or"

An implementation of HostLoadImportedModule must conform to the following requirements:

• The host environment must perform FinishLoadingImportedModule(referrer, specifier, payload, result), where result is either a normal completion containing the loaded Module Record or a throw completion, either synchronously or asynchronously.

(Emphasis added)

[bnoordhuis]

That's right.

[guest271314]

Good to know. I can throw specifications out of the window as meaning anything.