ix/src/asynciterable/operators/pluck.ts

The Interactive Extensions for JavaScript

import { AsyncIterableX } from '../asynciterablex.js';
import { map } from './map.js';
import { OperatorAsyncFunction } from '../../interfaces.js';

function plucker(props: string[], length: number): (x: any) => any {
  const mapper = (x: any) => {
    let currentProp = x;
    for (let i = 0; i < length; i++) {
      const p = currentProp[props[i]];
      if (typeof p !== 'undefined') {
        currentProp = p;
      } else {
        return undefined;
      }
    }
    return currentProp;
  };

  return mapper;
}

/**
 * Maps each source value to its specified nested property.
 *
 * @template TSource The type of the elements in the source sequence.
 * @template TResult The type of the elements in the result sequence, obtained by the property names.
 * @param {...string[]} args The nested properties to pluck from each source value.
 * @returns {OperatorAsyncFunction<TSource, TResult>} An async-iterable of property values from the source values.
 */
export function pluck<TSource, TResult>(
  ...args: string[]
): OperatorAsyncFunction<TSource, TResult> {
  return function pluckOperatorFunction(source: AsyncIterable<TSource>): AsyncIterableX<TResult> {
    return map<TSource, TResult>(
      (plucker(args, args.length) as any) as (value: TSource) => TResult
    )(source);
  };
}