Function map

lib/utils.js:737–739

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

(arr, fn, callback)

 * @param {Function} [callback]
 */
function map(arr, fn, callback) {
  return mapEach(arr, fn, false, callback);
}

function mapEach(arr, fn, useIndex, callback) {
  if (!Array.isArray(arr)) {