headers.keys() does not return an iterator

[nabetti1720]

I thought that in DelSkayn/rquickjs#564 it became possible to return an iterator from Rust to JavaScript, so I tried the following implementation, but it doesn't work as expected.

pub fn keys<'js>(&self, ctx: Ctx<'js>) -> Result<Value<'js>> {
    let iter = self
        .headers
        .iter()
        .map(|(k, _)| k.as_ref().to_owned())
        .collect::<Vec<_>>();

    Iterable::from(iter).into_js(&ctx)
}

Test pattern used to check operation:

// reproduction.js
function run() {
  const headers = new Headers([
    ['x-first', '1'],
    ['x-second', '2'],
  ]);

  const iter = headers.keys();

  console.log('typeof iter[Symbol.iterator]:', typeof iter[Symbol.iterator]);

  console.log(
    'iter[Symbol.iterator]() === iter:',
    iter[Symbol.iterator]() === iter
  );

  const collected = [];
  for (const k of headers.keys()) {
    collected.push(k);
  }
  console.log('for..of result:', collected);

  const spread = [...headers.keys()];
  console.log('spread result:', spread);

  console.log('--- iterator.next() ---');

  const iter2 = headers.keys();
  let step;

  step = iter2.next();
  console.log('next #1:', step);  // { value: 'x-first', done: false }

  step = iter2.next();
  console.log('next #2:', step);  // { value: 'x-second', done: false }

  step = iter2.next();
  console.log('next #3:', step);  // { value: undefined, done: true }

  step = iter2.next();
  console.log('next #4:', step);  // { value: undefined, done: true }
}

run();

The output is as follows:

% node ./reproduction.js
typeof iter[Symbol.iterator]: function
iter[Symbol.iterator]() === iter: true
for..of result: [ 'x-first', 'x-second' ]
spread result: [ 'x-first', 'x-second' ]
--- iterator.next() ---
next #1: { value: 'x-first', done: false }
next #2: { value: 'x-second', done: false }
next #3: { value: undefined, done: true }
next #4: { value: undefined, done: true }


% llrt ./reproduction.js
typeof iter[Symbol.iterator]: function
iter[Symbol.iterator]() === iter: false
for..of result: [ 'x-first', 'x-second' ]
spread result: [ 'x-first', 'x-second' ]
--- iterator.next() ---
TypeError: not a function
  at run (/Users/shinya/Workspaces/llrt-test/reproduction.js:30:16)
      at <anonymous> (/Users/shinya/Workspaces/llrt-test/reproduction.js:43:1)

Am I missing something?