@graffy/common/esm/stream/mergeStreams.js

Common libraries that used by various Graffy modules.

import mergeIterators from 'merge-async-iterators';
import { merge } from '../graph';
export default async function* mergeStreams(...streams) {
  const firstValues = (await Promise.all(streams.map(stream => stream.next()))).map(iter => iter.value); // If even one is a change-only stream, the result is a change-only stream

  if (firstValues.some(value => typeof value === 'undefined')) {
    yield undefined;

    for (const value of firstValues) {
      if (typeof value !== 'undefined') yield value;
    }
  } else {
    let merged = [];

    for (const value of firstValues) merge(merged, value);

    yield merged;
  }

  yield* mergeIterators(streams);
}