Function mapSeries

lib/utils.js:790–832

* @param {Array} arr * @param {Function} fn * @param {Function} [callback]

(arr, fn, callback)

 * @param {Function} [callback]
 */
function mapSeries(arr, fn, callback) {
  if (!Array.isArray(arr)) {
    throw new TypeError('First parameter must be an Array');
  }
  callback = callback || noop;
  const length = arr.length;
  if (length === 0) {
    return callback(null, []);
  }
  const result = new Array(length);
  let index = 0;
  let sync;
  invoke(0);
  if (sync === undefined) {
    sync = false;
  }

  function invoke(i) {
    fn(arr[i], function mapItemCallback(err, transformed) {
      result[i] = transformed;
      next(err);
    });
  }

  function next(err) {
    if (err) {
      return callback(err);
    }
    if (++index === length) {
      return callback(null, result);
    }
    if (sync === undefined) {
      sync = true;
    }
    const i = index;
    if (sync) {
      return process.nextTick(function () {
        invoke(i);
      });
    }
    invoke(index);
  }
}

/**
 * @param {Array.<Function>} arr