ix/src/asynciterable/defer.ts

The Interactive Extensions for JavaScript

import { AsyncIterableX } from './asynciterablex.js';
import { wrapWithAbort } from './operators/withabort.js';
import { throwIfAborted } from '../aborterror.js';

class DeferAsyncIterable<TSource> extends AsyncIterableX<TSource> {
  private _fn: (signal?: AbortSignal) => AsyncIterable<TSource> | Promise<AsyncIterable<TSource>>;

  constructor(
    fn: (signal?: AbortSignal) => AsyncIterable<TSource> | Promise<AsyncIterable<TSource>>
  ) {
    super();
    this._fn = fn;
  }

  async *[Symbol.asyncIterator](signal?: AbortSignal) {
    throwIfAborted(signal);
    const items = await this._fn(signal);
    for await (const item of wrapWithAbort(items, signal)) {
      yield item;
    }
  }
}

/**
 * Returns an async-iterable sequence that invokes the specified factory function whenever a call to [Symbol.asyncIterator] has been made.
 *
 * @template TSource The type of the elements in the sequence returned by the factory function, and in the resulting sequence.
 * @param {((signal?: AbortSignal) => AsyncIterable<TSource> | Promise<AsyncIterable<TSource>>)} factory Async-iterable factory function to
 * invoke for each call to [Symbol.asyncIterator].
 * @returns {AsyncIterableX<TSource>} An async-iterable sequence whose observers trigger an invocation of the given async-iterable factory function.
 */
export function defer<TSource>(
  factory: (signal?: AbortSignal) => AsyncIterable<TSource> | Promise<AsyncIterable<TSource>>
): AsyncIterableX<TSource> {
  return new DeferAsyncIterable<TSource>(factory);
}