tryEach.js

import noop from 'lodash/noop';
import eachSeries from './eachSeries';
import wrapAsync from './internal/wrapAsync';
import slice from './internal/slice';

/**
 * It runs each task in series but stops whenever any of the functions were
 * successful. If one of the tasks were successful, the `callback` will be
 * passed the result of the successful task. If all tasks fail, the callback
 * will be passed the error and result (if any) of the final attempt.
 *
 * @name tryEach
 * @static
 * @memberOf module:ControlFlow
 * @method
 * @category Control Flow
 * @param {Array|Iterable|Object} tasks - A collection containing functions to
 * run, each function is passed a `callback(err, result)` it must call on
 * completion with an error `err` (which can be `null`) and an optional `result`
 * value.
 * @param {Function} [callback] - An optional callback which is called when one
 * of the tasks has succeeded, or all have failed. It receives the `err` and
 * `result` arguments of the last attempt at completing the `task`. Invoked with
 * (err, results).
 * @example
 * async.tryEach([
 *     function getDataFromFirstWebsite(callback) {
 *         // Try getting the data from the first website
 *         callback(err, data);
 *     },
 *     function getDataFromSecondWebsite(callback) {
 *         // First website failed,
 *         // Try getting the data from the backup website
 *         callback(err, data);
 *     }
 * ],
 * // optional callback
 * function(err, results) {
 *     Now do something with the data.
 * });
 *
 */
export default function tryEach(tasks, callback) {
    var error = null;
    var result;
    callback = callback || noop;
    eachSeries(tasks, function(task, callback) {
        wrapAsync(task)(function (err, res/*, ...args*/) {
            if (arguments.length > 2) {
                result = slice(arguments, 1);
            } else {
                result = res;
            }
            error = err;
            callback(!err);
        });
    }, function () {
        callback(error, result);
    });
}