Bug: interopDefault proxy returns bound functions, breaking native await using (Node 24+) #437

Summary

interopDefault in src/utils.ts:151-156 wraps fall-through methods with Function.prototype.bind to preserve this for the underlying default export. When the property accessed is Symbol.asyncDispose / Symbol.dispose and the consumer uses native await using / using (Node 24+, no jiti transpilation of the calling file), V8 rejects the bound function returned through the proxy get trap with:

TypeError: Symbol(Symbol.asyncDispose) is not a function

This does not surface when the calling file is itself transpiled by jiti, because Babel rewrites await using to a DisposableStack helper that calls the bound function directly.

Minimal repro (no jiti)

// repro.mjs — Node 24+
const def = { [Symbol.asyncDispose]: async () => console.log("disposed!") };

const proxy = new Proxy({ default: def }, {
  get(t, prop) {
    if (prop === Symbol.asyncDispose) return def[Symbol.asyncDispose].bind(def);
  },
});

console.log("manual lookup ok:", proxy[Symbol.asyncDispose]); // works
{
  await using x = proxy; // throws: Symbol(Symbol.asyncDispose) is not a function
}

Replacing .bind(def) with an arrow wrapper makes V8 accept it:

get(t, prop) {
  if (prop === Symbol.asyncDispose) {
    const fn = def[Symbol.asyncDispose];
    return (...args) => fn.apply(def, args);
  }
}

End-to-end repro (with jiti)

// db.ts
class DB {
  async query(sql: string) { console.log(`[db.query] ${sql}`); }
  async [Symbol.asyncDispose]() { console.log("[db] disposed"); }
}
export default new DB();

// run.ts
import { createJiti } from "jiti";
const jiti = createJiti(import.meta.url);
await using db = await jiti.import("./db.ts");
await db.query("SELECT 1");

• node run.ts (Node 24.10 with --experimental-strip-types / native TS) → throws TypeError: Symbol(Symbol.asyncDispose) is not a function
• node lib/jiti-cli.mjs run.ts → works (Babel transpiles await using)

Workaround

Bypass the proxy by reading .default directly, or use the default: true option:

await using db = (await jiti.import("./db.ts")).default;
// or
await using db = await jiti.import("./db.ts", { default: true });

Suggested fix

In interopDefault, replace value.bind(def) with an arrow wrapper for the fall-through case:

- if (typeof value === "function") {
-   value = value.bind(def);
- }
+ if (typeof value === "function") {
+   const fn = value;
+   value = (...args: any[]) => fn.apply(def, args);
+ }

Environment

• Node v24.10.0 (also reproduces on v25.5.0)
• jiti main (post-2.7.0)