ix/src/asynciterable/operators/map.ts

The Interactive Extensions for JavaScript

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

/** @ignore */
export class MapAsyncIterable<TSource, TResult> extends AsyncIterableX<TResult> {
  private _source: AsyncIterable<TSource>;
  private _selector: (
    value: TSource,
    index: number,
    signal?: AbortSignal
  ) => Promise<TResult> | TResult;
  private _thisArg: any;

  constructor(
    source: AsyncIterable<TSource>,
    selector: (value: TSource, index: number, signal?: AbortSignal) => Promise<TResult> | TResult,
    thisArg?: any
  ) {
    super();
    this._source = source;
    this._selector = selector;
    this._thisArg = thisArg;
  }

  async *[Symbol.asyncIterator](signal?: AbortSignal) {
    throwIfAborted(signal);
    let i = 0;
    for await (const item of wrapWithAbort(this._source, signal)) {
      const result = await this._selector.call(this._thisArg, item, i++, signal);
      yield result;
    }
  }
}

/**
 * Projects each element of an async-enumerable sequence into a new form.
 *
 * @template TSource The type of the elements in the source sequence.
 * @template TResult The type of the elements in the result sequence, obtained by running the selector
 * function for each element in the source sequence.
 * @param {((value: TSource, index: number, signal?: AbortSignal) => Promise<TResult> | TResult)} selector A transform function
 * to apply to each source element.
 * @param {*} [thisArg] Optional this for binding to the selector.
 * @returns {OperatorAsyncFunction<TSource, TResult>} An async-iterable sequence whose elements are the result of invoking the transform
 * function on each element of source.
 */
export function map<TSource, TResult>(
  selector: (value: TSource, index: number, signal?: AbortSignal) => Promise<TResult> | TResult,
  thisArg?: any
): OperatorAsyncFunction<TSource, TResult> {
  return function mapOperatorFunction(source: AsyncIterable<TSource>): AsyncIterableX<TResult> {
    return new MapAsyncIterable<TSource, TResult>(source, selector, thisArg);
  };
}