ix/src/asynciterable/asyncifyerrback.ts

The Interactive Extensions for JavaScript

import { AsyncIterableX } from './asynciterablex.js';
import { AsyncSink } from './asyncsink.js';
import { memoize } from './operators/memoize.js';

/**
 * Converts a Node.js style error first callback to an async-iterable sequence.
 *
 * @template TSource The type of the returned value from the callback.
 * @param {Function} func The Node.js error first callback to convert to an async-iterable.
 * @returns {(...args: any[]) => AsyncIterableX<TSource>} A function, when invoked, contains the result of the callback as an async-iterable.
 */
export function asyncifyErrback<TSource>(
  func: (...xs: any[]) => any
): (...args: any[]) => AsyncIterableX<TSource> {
  return function (...args: any[]) {
    const sink = new AsyncSink<TSource>();

    const handler = function (err: any, ...innerArgs: any[]) {
      if (err) {
        sink.error(err);
        sink.end();
      } else {
        sink.write(innerArgs.length === 1 ? innerArgs[0] : innerArgs);
        sink.end();
      }
    };

    try {
      func(...args.concat(handler));
    } catch (e) {
      sink.error(e);
      sink.end();
    }

    const yielder = async function* () {
      for (let next; !(next = await sink.next()).done; ) {
        yield next.value;
      }
    };

    return memoize<TSource>()(yielder());
  };
}