eachOf.js

import isArrayLike from 'lodash/isArrayLike';

import breakLoop from './internal/breakLoop';
import eachOfLimit from './eachOfLimit';
import doLimit from './internal/doLimit';
import noop from 'lodash/noop';
import once from './internal/once';
import onlyOnce from './internal/onlyOnce';

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

    function iteratorCallback(err, value) {
        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.
var eachOfGeneric = doLimit(eachOfLimit, Infinity);

/**
 * 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|Object} coll - A collection to iterate over.
 * @param {Function} 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. The iteratee is passed a `callback(err)` which must be called once it
 * has completed. If no error has occurred, the callback should be run without
 * arguments or with an explicit `null` argument. 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).
 * @example
 *
 * var obj = {dev: "/dev.json", test: "/test.json", prod: "/prod.json"};
 * var configs = {};
 *
 * async.forEachOf(obj, function (value, key, callback) {
 *     fs.readFile(__dirname + value, "utf8", function (err, data) {
 *         if (err) return callback(err);
 *         try {
 *             configs[key] = JSON.parse(data);
 *         } catch (e) {
 *             return callback(e);
 *         }
 *         callback();
 *     });
 * }, function (err) {
 *     if (err) console.error(err.message);
 *     // configs is now a map of JSON data
 *     doSomethingWith(configs);
 * });
 */
export default function(coll, iteratee, callback) {
    var eachOfImplementation = isArrayLike(coll) ? eachOfArrayLike : eachOfGeneric;
    eachOfImplementation(coll, iteratee, callback);
}