This repo is created to demonstrate a bug in the Babel 7 async iteration plugin.

First clone locally.

Then install the dependencies:

npm i

Then you can either use babel node to run the example: npm start

Or you can build using npm run build and then run the built file via npm start:dist

Below is the contents of src/index.js file:

import '@babel/polyfill'; // Don't copy this line if you are going to run it in Chrome

async function* inner() {
  const ids = [0, 1, 2, 3];
  for await (const id of ids) {
    yield id;
  }
}

async function* wrapper() {
  yield* inner();
  console.log('done');
}

const run = async() => {
  for await (const id of wrapper()) {
    console.log(id);
    break;
  }
};

run();

If you run the above code in the Chrome console, you get:

0

When you use Babel, you get:

0
'done'

When for await is used on a generator that uses yield* to delegate to another generator and we attempt to break out of the loop, the iteration stops but the code after yield* still runs which is why we get done. This is wrong and the native implementation in v8 doesn't have this problem.