jQuery ajax/deferred `Promise.allSettled`

deferAllSettled.js

/**
 * @typedef {{ status: 'fulfilled', value: *}} TPromiseAllSettledFulfilledResult
 * @typedef {{ status: 'rejected', reason: (*|Error) }} TPromiseAllSettledRejectedResult
 * @typedef {(TPromiseAllSettledFulfilledResult|TPromiseAllSettledRejectedResult)[]} TDeferAllSettledResult
 */

/**
 * Same as `Promise.allSettled`.
 * Try hard to not to use `Promise`, all from JQuery.
 * @param deferIterator {JQuery.Deferred[]|JQuery.jqXHR[]|Object<string, JQuery.Deferred>}
 * @return {JQuery.Deferred<TDeferAllSettledResult>}
 */
function deferAllSettled (deferIterator) {
  /**
   * Internal. This will be returned out to identify all deferInstance resolved/rejected.
   * @param {JQuery.Deferred} dtd
   * @return {JQuery.Deferred}
   */
  function _deferAllSettled (dtd) {
    /**
     * @type {JQuery.Deferred<*>[]}
     */
    const iteratorArr = Object.values(deferIterator);
    let len = iteratorArr.length;
    const result = new Array(len);

    if (!len) return dtd.resolve(result);

    iteratorArr.forEach(function (iterator, index) {
      iterator
        .then(function (value) {
          return result[index] = {
            status: 'fulfilled',
            value
          };
        })
        .catch(function (reason) {
          return result[index] = {
            status: 'rejected',
            reason
          };
        })
        .always(function () {
          len--;

          // If all executed and got the result or reason.
          if (!len) {
            return dtd.resolve(result);
          }
        });
    });

    return dtd;
  }

  return $.when(_deferAllSettled($.Deferred()));
}