Function resolveList

packages/context/src/value-promise.ts:157–183

(
  list: T[],
  resolver: (val: T, index: number, values: T[]) => ValueOrPromise<V>,
)

 * be invoked with the property value, the property index, and the source array.
 */
export function resolveList<T, V>(
  list: T[],
  resolver: (val: T, index: number, values: T[]) => ValueOrPromise<V>,
): ValueOrPromise<V[]> {
  const result: V[] = new Array<V>(list.length);
  let asyncResolvers: PromiseLike<void>[] | undefined = undefined;

  const setter = (index: number) => (val: V) => {
    result[index] = val;
  };

  for (let ix = 0; ix < list.length; ix++) {
    const valueOrPromise = resolver(list[ix], ix, list);
    if (isPromiseLike(valueOrPromise)) {
      if (!asyncResolvers) asyncResolvers = [];
      asyncResolvers.push(valueOrPromise.then(setter(ix)));
    } else {
      result[ix] = valueOrPromise;
    }
  }

  if (asyncResolvers) {
    return Promise.all(asyncResolvers).then(() => result);
  } else {
    return result;
  }
}

/**
 * Try to run an action that returns a promise or a value