/** @module promiseQueue */
/**
 * @classdesc Creates a queue of functions that are guaranteed to be run
 * exactly once and in serial FIFO order. So that the first enqueue function
 * will complete before the second is executed.
 *
 * ```javascript
 * var PromiseQueue = require('promiseQueue');
 * var promiseQueue = new PromiseQueue();
 * var firstPromise = promiseQueue.enqueue(function(resolve, reject) {
 *    do stuff...
 * }).then(function(result) {
 *    do more stuff...
 * }).catch(function(err) {
 *    and more stuff...
 * });
 * ```
 *
 * @public
 * @constructor
 */
export default function PromiseQueue(): void;