async1_fromCallback.js

function fromCallback(emitter) {
  let values;
  let resolve;
  const init = r => [values, resolve] = [[], r];  
  let valuesAvailable = new Promise(init);
  emitter(value => {
    values.push(value);
    resolve(values);
  });
  return {
    [Symbol.asyncIterator]: async function*() {
      for (;;) {
        const vs = await valuesAvailable;
        valuesAvailable = new Promise(init);
        yield* vs;
      }
    }
  };
}