async.js

(function (global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
    typeof define === 'function' && define.amd ? define(['exports'], factory) :
    (factory((global.async = {})));
}(this, (function (exports) { 'use strict';

    /**
     * Creates a continuation function with some arguments already applied.
     *
     * Useful as a shorthand when combined with other control flow functions. Any
     * arguments passed to the returned function are added to the arguments
     * originally passed to apply.
     *
     * @name apply
     * @static
     * @memberOf module:Utils
     * @method
     * @category Util
     * @param {Function} fn - The function you want to eventually apply all
     * arguments to. Invokes with (arguments...).
     * @param {...*} arguments... - Any number of arguments to automatically apply
     * when the continuation is called.
     * @returns {Function} the partially-applied function
     * @example
     *
     * // using apply
     * async.parallel([
     *     async.apply(fs.writeFile, 'testfile1', 'test1'),
     *     async.apply(fs.writeFile, 'testfile2', 'test2')
     * ]);
     *
     *
     * // the same process without using apply
     * async.parallel([
     *     function(callback) {
     *         fs.writeFile('testfile1', 'test1', callback);
     *     },
     *     function(callback) {
     *         fs.writeFile('testfile2', 'test2', callback);
     *     }
     * ]);
     *
     * // It's possible to pass any number of additional arguments when calling the
     * // continuation:
     *
     * node> var fn = async.apply(sys.puts, 'one');
     * node> fn('two', 'three');
     * one
     * two
     * three
     */
    function apply(fn, ...args) {
        return (...callArgs) => fn(...args,...callArgs);
    }

    function initialParams (fn) {
        return function (...args/*, callback*/) {
            var callback = args.pop();
            return fn.call(this, args, callback);
        };
    }

    /* istanbul ignore file */

    var hasQueueMicrotask = typeof queueMicrotask === 'function' && queueMicrotask;
    var hasSetImmediate = typeof setImmediate === 'function' && setImmediate;
    var hasNextTick = typeof process === 'object' && typeof process.nextTick === 'function';

    function fallback(fn) {
        setTimeout(fn, 0);
    }

    function wrap(defer) {
        return (fn, ...args) => defer(() => fn(...args));
    }

    var _defer;

    if (hasQueueMicrotask) {
        _defer = queueMicrotask;
    } else if (hasSetImmediate) {
        _defer = setImmediate;
    } else if (hasNextTick) {
        _defer = process.nextTick;
    } else {
        _defer = fallback;
    }

    var setImmediate$1 = wrap(_defer);

    /**
     * Take a sync function and make it async, passing its return value to a
     * callback. This is useful for plugging sync functions into a waterfall,
     * series, or other async functions. Any arguments passed to the generated
     * function will be passed to the wrapped function (except for the final
     * callback argument). Errors thrown will be passed to the callback.
     *
     * If the function passed to `asyncify` returns a Promise, that promises's
     * resolved/rejected state will be used to call the callback, rather than simply
     * the synchronous return value.
     *
     * This also means you can asyncify ES2017 `async` functions.
     *
     * @name asyncify
     * @static
     * @memberOf module:Utils
     * @method
     * @alias wrapSync
     * @category Util
     * @param {Function} func - The synchronous function, or Promise-returning
     * function to convert to an {@link AsyncFunction}.
     * @returns {AsyncFunction} An asynchronous wrapper of the `func`. To be
     * invoked with `(args..., callback)`.
     * @example
     *
     * // passing a regular synchronous function
     * async.waterfall([
     *     async.apply(fs.readFile, filename, "utf8"),
     *     async.asyncify(JSON.parse),
     *     function (data, next) {
     *         // data is the result of parsing the text.
     *         // If there was a parsing error, it would have been caught.
     *     }
     * ], callback);
     *
     * // passing a function returning a promise
     * async.waterfall([
     *     async.apply(fs.readFile, filename, "utf8"),
     *     async.asyncify(function (contents) {
     *         return db.model.create(contents);
     *     }),
     *     function (model, next) {
     *         // `model` is the instantiated model object.
     *         // If there was an error, this function would be skipped.
     *     }
     * ], callback);
     *
     * // es2017 example, though `asyncify` is not needed if your JS environment
     * // supports async functions out of the box
     * var q = async.queue(async.asyncify(async function(file) {
     *     var intermediateStep = await processFile(file);
     *     return await somePromise(intermediateStep)
     * }));
     *
     * q.push(files);
     */
    function asyncify(func) {
        if (isAsync(func)) {
            return function (...args/*, callback*/) {
                const callback = args.pop();
                const promise = func.apply(this, args);
                return handlePromise(promise, callback)
            }
        }

        return initialParams(function (args, callback) {
            var result;
            try {
                result = func.apply(this, args);
            } catch (e) {
                return callback(e);
            }
            // if result is Promise object
            if (result && typeof result.then === 'function') {
                return handlePromise(result, callback)
            } else {
                callback(null, result);
            }
        });
    }

    function handlePromise(promise, callback) {
        return promise.then(value => {
            invokeCallback(callback, null, value);
        }, err => {
            invokeCallback(callback, err && err.message ? err : new Error(err));
        });
    }

    function invokeCallback(callback, error, value) {
        try {
            callback(error, value);
        } catch (err) {
            setImmediate$1(e => { throw e }, err);
        }
    }

    function isAsync(fn) {
        return fn[Symbol.toStringTag] === 'AsyncFunction';
    }

    function isAsyncGenerator(fn) {
        return fn[Symbol.toStringTag] === 'AsyncGenerator';
    }

    function isAsyncIterable(obj) {
        return typeof obj[Symbol.asyncIterator] === 'function';
    }

    function wrapAsync(asyncFn) {
        if (typeof asyncFn !== 'function') throw new Error('expected a function')
        return isAsync(asyncFn) ? asyncify(asyncFn) : asyncFn;
    }

    // conditionally promisify a function.
    // only return a promise if a callback is omitted
    function awaitify (asyncFn, arity = asyncFn.length) {
        if (!arity) throw new Error('arity is undefined')
        function awaitable (...args) {
            if (typeof args[arity - 1] === 'function') {
                return asyncFn.apply(this, args)
            }

            return new Promise((resolve, reject) => {
                args[arity - 1] = (err, ...cbArgs) => {
                    if (err) return reject(err)
                    resolve(cbArgs.length > 1 ? cbArgs : cbArgs[0]);
                };
                asyncFn.apply(this, args);
            })
        }

        return awaitable
    }

    function applyEach (eachfn) {
        return function applyEach(fns, ...callArgs) {
            const go = awaitify(function (callback) {
                var that = this;
                return eachfn(fns, (fn, cb) => {
                    wrapAsync(fn).apply(that, callArgs.concat(cb));
                }, callback);
            });
            return go;
        };
    }

    function _asyncMap(eachfn, arr, iteratee, callback) {
        arr = arr || [];
        var results = [];
        var counter = 0;
        var _iteratee = wrapAsync(iteratee);

        return eachfn(arr, (value, _, iterCb) => {
            var index = counter++;
            _iteratee(value, (err, v) => {
                results[index] = v;
                iterCb(err);
            });
        }, err => {
            callback(err, results);
        });
    }

    function isArrayLike(value) {
        return value &&
            typeof value.length === 'number' &&
            value.length >= 0 &&
            value.length % 1 === 0;
    }

    // A temporary value used to identify if the loop should be broken.
    // See #1064, #1293
    const breakLoop = {};

    function once(fn) {
        function wrapper (...args) {
            if (fn === null) return;
            var callFn = fn;
            fn = null;
            callFn.apply(this, args);
        }
        Object.assign(wrapper, fn);
        return wrapper
    }

    function getIterator (coll) {
        return coll[Symbol.iterator] && coll[Symbol.iterator]();
    }

    function createArrayIterator(coll) {
        var i = -1;
        var len = coll.length;
        return function next() {
            return ++i < len ? {value: coll[i], key: i} : null;
        }
    }

    function createES2015Iterator(iterator) {
        var i = -1;
        return function next() {
            var item = iterator.next();
            if (item.done)
                return null;
            i++;
            return {value: item.value, key: i};
        }
    }

    function createObjectIterator(obj) {
        var okeys = obj ? Object.keys(obj) : [];
        var i = -1;
        var len = okeys.length;
        return function next() {
            var key = okeys[++i];
            if (key === '__proto__') {
                return next();
            }
            return i < len ? {value: obj[key], key} : null;
        };
    }

    function createIterator(coll) {
        if (isArrayLike(coll)) {
            return createArrayIterator(coll);
        }

        var iterator = getIterator(coll);
        return iterator ? createES2015Iterator(iterator) : createObjectIterator(coll);
    }

    function onlyOnce(fn) {
        return function (...args) {
            if (fn === null) throw new Error("Callback was already called.");
            var callFn = fn;
            fn = null;
            callFn.apply(this, args);
        };
    }

    // for async generators
    function asyncEachOfLimit(generator, limit, iteratee, callback) {
        let done = false;
        let canceled = false;
        let awaiting = false;
        let running = 0;
        let idx = 0;

        function replenish() {
            //console.log('replenish')
            if (running >= limit || awaiting || done) return
            //console.log('replenish awaiting')
            awaiting = true;
            generator.next().then(({value, done: iterDone}) => {
                //console.log('got value', value)
                if (canceled || done) return
                awaiting = false;
                if (iterDone) {
                    done = true;
                    if (running <= 0) {
                        //console.log('done nextCb')
                        callback(null);
                    }
                    return;
                }
                running++;
                iteratee(value, idx, iterateeCallback);
                idx++;
                replenish();
            }).catch(handleError);
        }

        function iterateeCallback(err, result) {
            //console.log('iterateeCallback')
            running -= 1;
            if (canceled) return
            if (err) return handleError(err)

            if (err === false) {
                done = true;
                canceled = true;
                return
            }

            if (result === breakLoop || (done && running <= 0)) {
                done = true;
                //console.log('done iterCb')
                return callback(null);
            }
            replenish();
        }

        function handleError(err) {
            if (canceled) return
            awaiting = false;
            done = true;
            callback(err);
        }

        replenish();
    }

    var eachOfLimit = (limit) => {
        return (obj, iteratee, callback) => {
            callback = once(callback);
            if (limit <= 0) {
                throw new RangeError('concurrency limit cannot be less than 1')
            }
            if (!obj) {
                return callback(null);
            }
            if (isAsyncGenerator(obj)) {
                return asyncEachOfLimit(obj, limit, iteratee, callback)
            }
            if (isAsyncIterable(obj)) {
                return asyncEachOfLimit(obj[Symbol.asyncIterator](), limit, iteratee, callback)
            }
            var nextElem = createIterator(obj);
            var done = false;
            var canceled = false;
            var running = 0;
            var looping = false;

            function iterateeCallback(err, value) {
                if (canceled) return
                running -= 1;
                if (err) {
                    done = true;
                    callback(err);
                }
                else if (err === false) {
                    done = true;
                    canceled = true;
                }
                else if (value === breakLoop || (done && running <= 0)) {
                    done = true;
                    return callback(null);
                }
                else if (!looping) {
                    replenish();
                }
            }

            function replenish () {
                looping = true;
                while (running < limit && !done) {
                    var elem = nextElem();
                    if (elem === null) {
                        done = true;
                        if (running <= 0) {
                            callback(null);
                        }
                        return;
                    }
                    running += 1;
                    iteratee(elem.value, elem.key, onlyOnce(iterateeCallback));
                }
                looping = false;
            }

            replenish();
        };
    };

    /**
     * The same as [`eachOf`]{@link module:Collections.eachOf} but runs a maximum of `limit` async operations at a
     * time.
     *
     * @name eachOfLimit
     * @static
     * @memberOf module:Collections
     * @method
     * @see [async.eachOf]{@link module:Collections.eachOf}
     * @alias forEachOfLimit
     * @category Collection
     * @param {Array|Iterable|AsyncIterable|Object} coll - A collection to iterate over.
     * @param {number} limit - The maximum number of async operations at a time.
     * @param {AsyncFunction} iteratee - An async function to apply to each
     * item in `coll`. The `key` is the item's key, or index in the case of an
     * array.
     * Invoked with (item, key, callback).
     * @param {Function} [callback] - A callback which is called when all
     * `iteratee` functions have finished, or an error occurs. Invoked with (err).
     * @returns {Promise} a promise, if a callback is omitted
     */
    function eachOfLimit$1(coll, limit, iteratee, callback) {
        return eachOfLimit(limit)(coll, wrapAsync(iteratee), callback);
    }

    var eachOfLimit$2 = awaitify(eachOfLimit$1, 4);

    // eachOf implementation optimized for array-likes
    function eachOfArrayLike(coll, iteratee, callback) {
        callback = once(callback);
        var index = 0,
            completed = 0,
            {length} = coll,
            canceled = false;
        if (length === 0) {
            callback(null);
        }

        function iteratorCallback(err, value) {
            if (err === false) {
                canceled = true;
            }
            if (canceled === true) return
            if (err) {
                callback(err);
            } else if ((++completed === length) || value === breakLoop) {
                callback(null);
            }
        }

        for (; index < length; index++) {
            iteratee(coll[index], index, onlyOnce(iteratorCallback));
        }
    }

    // a generic version of eachOf which can handle array, object, and iterator cases.
    function eachOfGeneric (coll, iteratee, callback) {
        return eachOfLimit$2(coll, Infinity, iteratee, callback);
    }

    /**
     * Like [`each`]{@link module:Collections.each}, except that it passes the key (or index) as the second argument
     * to the iteratee.
     *
     * @name eachOf
     * @static
     * @memberOf module:Collections
     * @method
     * @alias forEachOf
     * @category Collection
     * @see [async.each]{@link module:Collections.each}
     * @param {Array|Iterable|AsyncIterable|Object} coll - A collection to iterate over.
     * @param {AsyncFunction} iteratee - A function to apply to each
     * item in `coll`.
     * The `key` is the item's key, or index in the case of an array.
     * Invoked with (item, key, callback).
     * @param {Function} [callback] - A callback which is called when all
     * `iteratee` functions have finished, or an error occurs. Invoked with (err).
     * @returns {Promise} a promise, if a callback is omitted
     * @example
     *
     * // dev.json is a file containing a valid json object config for dev environment
     * // dev.json is a file containing a valid json object config for test environment
     * // prod.json is a file containing a valid json object config for prod environment
     * // invalid.json is a file with a malformed json object
     *
     * let configs = {}; //global variable
     * let validConfigFileMap = {dev: 'dev.json', test: 'test.json', prod: 'prod.json'};
     * let invalidConfigFileMap = {dev: 'dev.json', test: 'test.json', invalid: 'invalid.json'};
     *
     * // asynchronous function that reads a json file and parses the contents as json object
     * function parseFile(file, key, callback) {
     *     fs.readFile(file, "utf8", function(err, data) {
     *         if (err) return calback(err);
     *         try {
     *             configs[key] = JSON.parse(data);
     *         } catch (e) {
     *             return callback(e);
     *         }
     *         callback();
     *     });
     * }
     *
     * // Using callbacks
     * async.forEachOf(validConfigFileMap, parseFile, function (err) {
     *     if (err) {
     *         console.error(err);
     *     } else {
     *         console.log(configs);
     *         // configs is now a map of JSON data, e.g.
     *         // { dev: //parsed dev.json, test: //parsed test.json, prod: //parsed prod.json}
     *     }
     * });
     *
     * //Error handing
     * async.forEachOf(invalidConfigFileMap, parseFile, function (err) {
     *     if (err) {
     *         console.error(err);
     *         // JSON parse error exception
     *     } else {
     *         console.log(configs);
     *     }
     * });
     *
     * // Using Promises
     * async.forEachOf(validConfigFileMap, parseFile)
     * .then( () => {
     *     console.log(configs);
     *     // configs is now a map of JSON data, e.g.
     *     // { dev: //parsed dev.json, test: //parsed test.json, prod: //parsed prod.json}
     * }).catch( err => {
     *     console.error(err);
     * });
     *
     * //Error handing
     * async.forEachOf(invalidConfigFileMap, parseFile)
     * .then( () => {
     *     console.log(configs);
     * }).catch( err => {
     *     console.error(err);
     *     // JSON parse error exception
     * });
     *
     * // Using async/await
     * async () => {
     *     try {
     *         let result = await async.forEachOf(validConfigFileMap, parseFile);
     *         console.log(configs);
     *         // configs is now a map of JSON data, e.g.
     *         // { dev: //parsed dev.json, test: //parsed test.json, prod: //parsed prod.json}
     *     }
     *     catch (err) {
     *         console.log(err);
     *     }
     * }
     *
     * //Error handing
     * async () => {
     *     try {
     *         let result = await async.forEachOf(invalidConfigFileMap, parseFile);
     *         console.log(configs);
     *     }
     *     catch (err) {
     *         console.log(err);
     *         // JSON parse error exception
     *     }
     * }
     *
     */
    function eachOf(coll, iteratee, callback) {
        var eachOfImplementation = isArrayLike(coll) ? eachOfArrayLike : eachOfGeneric;
        return eachOfImplementation(coll, wrapAsync(iteratee), callback);
    }

    var eachOf$1 = awaitify(eachOf, 3);

    /**
     * Produces a new collection of values by mapping each value in `coll` through
     * the `iteratee` function. The `iteratee` is called with an item from `coll`
     * and a callback for when it has finished processing. Each of these callbacks
     * takes 2 arguments: an `error`, and the transformed item from `coll`. If
     * `iteratee` passes an error to its callback, the main `callback` (for the
     * `map` function) is immediately called with the error.
     *
     * Note, that since this function applies the `iteratee` to each item in
     * parallel, there is no guarantee that the `iteratee` functions will complete
     * in order. However, the results array will be in the same order as the
     * original `coll`.
     *
     * If `map` is passed an Object, the results will be an Array.  The results
     * will roughly be in the order of the original Objects' keys (but this can
     * vary across JavaScript engines).
     *
     * @name map
     * @static
     * @memberOf module:Collections
     * @method
     * @category Collection
     * @param {Array|Iterable|AsyncIterable|Object} coll - A collection to iterate over.
     * @param {AsyncFunction} iteratee - An async function to apply to each item in
     * `coll`.
     * The iteratee should complete with the transformed item.
     * Invoked with (item, callback).
     * @param {Function} [callback] - A callback which is called when all `iteratee`
     * functions have finished, or an error occurs. Results is an Array of the
     * transformed items from the `coll`. Invoked with (err, results).
     * @returns {Promise} a promise, if no callback is passed
     * @example
     *
     * // file1.txt is a file that is 1000 bytes in size
     * // file2.txt is a file that is 2000 bytes in size
     * // file3.txt is a file that is 3000 bytes in size
     * // file4.txt does not exist
     *
     * const fileList = ['file1.txt','file2.txt','file3.txt'];
     * const withMissingFileList = ['file1.txt','file2.txt','file4.txt'];
     *
     * // asynchronous function that returns the file size in bytes
     * function getFileSizeInBytes(file, callback) {
     *     fs.stat(file, function(err, stat) {
     *         if (err) {
     *             return callback(err);
     *         }
     *         callback(null, stat.size);
     *     });
     * }
     *
     * // Using callbacks
     * async.map(fileList, getFileSizeInBytes, function(err, results) {
     *     if (err) {
     *         console.log(err);
     *     } else {
     *         console.log(results);
     *         // results is now an array of the file size in bytes for each file, e.g.
     *         // [ 1000, 2000, 3000]
     *     }
     * });
     *
     * // Error Handling
     * async.map(withMissingFileList, getFileSizeInBytes, function(err, results) {
     *     if (err) {
     *         console.log(err);
     *         // [ Error: ENOENT: no such file or directory ]
     *     } else {
     *         console.log(results);
     *     }
     * });
     *
     * // Using Promises
     * async.map(fileList, getFileSizeInBytes)
     * .then( results => {
     *     console.log(results);
     *     // results is now an array of the file size in bytes for each file, e.g.
     *     // [ 1000, 2000, 3000]
     * }).catch( err => {
     *     console.log(err);
     * });
     *
     * // Error Handling
     * async.map(withMissingFileList, getFileSizeInBytes)
     * .then( results => {
     *     console.log(results);
     * }).catch( err => {
     *     console.log(err);
     *     // [ Error: ENOENT: no such file or directory ]
     * });
     *
     * // Using async/await
     * async () => {
     *     try {
     *         let results = await async.map(fileList, getFileSizeInBytes);
     *         console.log(results);
     *         // results is now an array of the file size in bytes for each file, e.g.
     *         // [ 1000, 2000, 3000]
     *     }
     *     catch (err) {
     *         console.log(err);
     *     }
     * }
     *
     * // Error Handling
     * async () => {
     *     try {
     *         let results = await async.map(withMissingFileList, getFileSizeInBytes);
     *         console.log(results);
     *     }
     *     catch (err) {
     *         console.log(err);
     *         // [ Error: ENOENT: no such file or directory ]
     *     }
     * }
     *
     */
    function map (coll, iteratee, callback) {
        return _asyncMap(eachOf$1, coll, iteratee, callback)
    }
    var map$1 = awaitify(map, 3);

    /**
     * Applies the provided arguments to each function in the array, calling
     * `callback` after all functions have completed. If you only provide the first
     * argument, `fns`, then it will return a function which lets you pass in the
     * arguments as if it were a single function call. If more arguments are
     * provided, `callback` is required while `args` is still optional. The results
     * for each of the applied async functions are passed to the final callback
     * as an array.
     *
     * @name applyEach
     * @static
     * @memberOf module:ControlFlow
     * @method
     * @category Control Flow
     * @param {Array|Iterable|AsyncIterable|Object} fns - A collection of {@link AsyncFunction}s
     * to all call with the same arguments
     * @param {...*} [args] - any number of separate arguments to pass to the
     * function.
     * @param {Function} [callback] - the final argument should be the callback,
     * called when all functions have completed processing.
     * @returns {AsyncFunction} - Returns a function that takes no args other than
     * an optional callback, that is the result of applying the `args` to each
     * of the functions.
     * @example
     *
     * const appliedFn = async.applyEach([enableSearch, updateSchema], 'bucket')
     *
     * appliedFn((err, results) => {
     *     // results[0] is the results for `enableSearch`
     *     // results[1] is the results for `updateSchema`
     * });
     *
     * // partial application example:
     * async.each(
     *     buckets,
     *     async (bucket) => async.applyEach([enableSearch, updateSchema], bucket)(),
     *     callback
     * );
     */
    var applyEach$1 = applyEach(map$1);

    /**
     * The same as [`eachOf`]{@link module:Collections.eachOf} but runs only a single async operation at a time.
     *
     * @name eachOfSeries
     * @static
     * @memberOf module:Collections
     * @method
     * @see [async.eachOf]{@link module:Collections.eachOf}
     * @alias forEachOfSeries
     * @category Collection
     * @param {Array|Iterable|AsyncIterable|Object} coll - A collection to iterate over.
     * @param {AsyncFunction} iteratee - An async function to apply to each item in
     * `coll`.
     * Invoked with (item, key, callback).
     * @param {Function} [callback] - A callback which is called when all `iteratee`
     * functions have finished, or an error occurs. Invoked with (err).
     * @returns {Promise} a promise, if a callback is omitted
     */
    function eachOfSeries(coll, iteratee, callback) {
        return eachOfLimit$2(coll, 1, iteratee, callback)
    }
    var eachOfSeries$1 = awaitify(eachOfSeries, 3);

    /**
     * The same as [`map`]{@link module:Collections.map} but runs only a single async operation at a time.
     *
     * @name mapSeries
     * @static
     * @memberOf module:Collections
     * @method
     * @see [async.map]{@link module:Collections.map}
     * @category Collection
     * @param {Array|Iterable|AsyncIterable|Object} coll - A collection to iterate over.
     * @param {AsyncFunction} iteratee - An async function to apply to each item in
     * `coll`.
     * The iteratee should complete with the transformed item.
     * Invoked with (item, callback).
     * @param {Function} [callback] - A callback which is called when all `iteratee`
     * functions have finished, or an error occurs. Results is an array of the
     * transformed items from the `coll`. Invoked with (err, results).
     * @returns {Promise} a promise, if no callback is passed
     */
    function mapSeries (coll, iteratee, callback) {
        return _asyncMap(eachOfSeries$1, coll, iteratee, callback)
    }
    var mapSeries$1 = awaitify(mapSeries, 3);

    /**
     * The same as [`applyEach`]{@link module:ControlFlow.applyEach} but runs only a single async operation at a time.
     *
     * @name applyEachSeries
     * @static
     * @memberOf module:ControlFlow
     * @method
     * @see [async.applyEach]{@link module:ControlFlow.applyEach}
     * @category Control Flow
     * @param {Array|Iterable|AsyncIterable|Object} fns - A collection of {@link AsyncFunction}s to all
     * call with the same arguments
     * @param {...*} [args] - any number of separate arguments to pass to the
     * function.
     * @param {Function} [callback] - the final argument should be the callback,
     * called when all functions have completed processing.
     * @returns {AsyncFunction} - A function, that when called, is the result of
     * appling the `args` to the list of functions.  It takes no args, other than
     * a callback.
     */
    var applyEachSeries = applyEach(mapSeries$1);

    const PROMISE_SYMBOL = Symbol('promiseCallback');

    function promiseCallback () {
        let resolve, reject;
        function callback (err, ...args) {
            if (err) return reject(err)
            resolve(args.length > 1 ? args : args[0]);
        }

        callback[PROMISE_SYMBOL] = new Promise((res, rej) => {
            resolve = res,
            reject = rej;
        });

        return callback
    }

    /**
     * Determines the best order for running the {@link AsyncFunction}s in `tasks`, based on
     * their requirements. Each function can optionally depend on other functions
     * being completed first, and each function is run as soon as its requirements
     * are satisfied.
     *
     * If any of the {@link AsyncFunction}s pass an error to their callback, the `auto` sequence
     * will stop. Further tasks will not execute (so any other functions depending
     * on it will not run), and the main `callback` is immediately called with the
     * error.
     *
     * {@link AsyncFunction}s also receive an object containing the results of functions which
     * have completed so far as the first argument, if they have dependencies. If a
     * task function has no dependencies, it will only be passed a callback.
     *
     * @name auto
     * @static
     * @memberOf module:ControlFlow
     * @method
     * @category Control Flow
     * @param {Object} tasks - An object. Each of its properties is either a
     * function or an array of requirements, with the {@link AsyncFunction} itself the last item
     * in the array. The object's key of a property serves as the name of the task
     * defined by that property, i.e. can be used when specifying requirements for
     * other tasks. The function receives one or two arguments:
     * * a `results` object, containing the results of the previously executed
     *   functions, only passed if the task has any dependencies,
     * * a `callback(err, result)` function, which must be called when finished,
     *   passing an `error` (which can be `null`) and the result of the function's
     *   execution.
     * @param {number} [concurrency=Infinity] - An optional `integer` for
     * determining the maximum number of tasks that can be run in parallel. By
     * default, as many as possible.
     * @param {Function} [callback] - An optional callback which is called when all
     * the tasks have been completed. It receives the `err` argument if any `tasks`
     * pass an error to their callback. Results are always returned; however, if an
     * error occurs, no further `tasks` will be performed, and the results object
     * will only contain partial results. Invoked with (err, results).
     * @returns {Promise} a promise, if a callback is not passed
     * @example
     *
     * //Using Callbacks
     * async.auto({
     *     get_data: function(callback) {
     *         // async code to get some data
     *         callback(null, 'data', 'converted to array');
     *     },
     *     make_folder: function(callback) {
     *         // async code to create a directory to store a file in
     *         // this is run at the same time as getting the data
     *         callback(null, 'folder');
     *     },
     *     write_file: ['get_data', 'make_folder', function(results, callback) {
     *         // once there is some data and the directory exists,
     *         // write the data to a file in the directory
     *         callback(null, 'filename');
     *     }],
     *     email_link: ['write_file', function(results, callback) {
     *         // once the file is written let's email a link to it...
     *         callback(null, {'file':results.write_file, 'email':'user@example.com'});
     *     }]
     * }, function(err, results) {
     *     if (err) {
     *         console.log('err = ', err);
     *     }
     *     console.log('results = ', results);
     *     // results = {
     *     //     get_data: ['data', 'converted to array']
     *     //     make_folder; 'folder',
     *     //     write_file: 'filename'
     *     //     email_link: { file: 'filename', email: 'user@example.com' }
     *     // }
     * });
     *
     * //Using Promises
     * async.auto({
     *     get_data: function(callback) {
     *         console.log('in get_data');
     *         // async code to get some data
     *         callback(null, 'data', 'converted to array');
     *     },
     *     make_folder: function(callback) {
     *         console.log('in make_folder');
     *         // async code to create a directory to store a file in
     *         // this is run at the same time as getting the data
     *         callback(null, 'folder');
     *     },
     *     write_file: ['get_data', 'make_folder', function(results, callback) {
     *         // once there is some data and the directory exists,
     *         // write the data to a file in the directory
     *         callback(null, 'filename');
     *     }],
     *     email_link: ['write_file', function(results, callback) {
     *         // once the file is written let's email a link to it...
     *         callback(null, {'file':results.write_file, 'email':'user@example.com'});
     *     }]
     * }).then(results => {
     *     console.log('results = ', results);
     *     // results = {
     *     //     get_data: ['data', 'converted to array']
     *     //     make_folder; 'folder',
     *     //     write_file: 'filename'
     *     //     email_link: { file: 'filename', email: 'user@example.com' }
     *     // }
     * }).catch(err => {
     *     console.log('err = ', err);
     * });
     *
     * //Using async/await
     * async () => {
     *     try {
     *         let results = await async.auto({
     *             get_data: function(callback) {
     *                 // async code to get some data
     *                 callback(null, 'data', 'converted to array');
     *             },
     *             make_folder: function(callback) {
     *                 // async code to create a directory to store a file in
     *                 // this is run at the same time as getting the data
     *                 callback(null, 'folder');
     *             },
     *             write_file: ['get_data', 'make_folder', function(results, callback) {