ix/src/asynciterable/whiledo.ts

The Interactive Extensions for JavaScript

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

class WhileAsyncIterable<TSource> extends AsyncIterableX<TSource> {
  private _condition: (signal?: AbortSignal) => boolean | Promise<boolean>;
  private _source: AsyncIterable<TSource>;

  constructor(
    condition: (signal?: AbortSignal) => boolean | Promise<boolean>,
    source: AsyncIterable<TSource>
  ) {
    super();
    this._condition = condition;
    this._source = source;
  }

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

/**
 * Repeats the given source as long as the specified conditions holds, where
 * the condition is evaluated before each repeated source is iterated.
 *
 * @template TSource
 * @param {AsyncIterable<TSource>} source Source to repeat as long as the condition function evaluates to true.
 * @param {((signal?: AbortSignal) => boolean | Promise<boolean>)} condition Condition that will be evaluated before the source sequence is iterated.
 * @returns {AsyncIterableX<TSource>} An async-iterable which is repeated while the condition returns true.
 */
export function whileDo<TSource>(
  source: AsyncIterable<TSource>,
  condition: (signal?: AbortSignal) => boolean | Promise<boolean>
): AsyncIterableX<TSource> {
  return new WhileAsyncIterable<TSource>(condition, source);
}