added unit testing, and started implementing unit tests...phew

node_modules/async/sortBy.js

@@ -0,0 +1,91 @@
+'use strict';
+
+Object.defineProperty(exports, "__esModule", {
+    value: true
+});
+exports.default = sortBy;
+
+var _arrayMap = require('lodash/_arrayMap');
+
+var _arrayMap2 = _interopRequireDefault(_arrayMap);
+
+var _baseProperty = require('lodash/_baseProperty');
+
+var _baseProperty2 = _interopRequireDefault(_baseProperty);
+
+var _map = require('./map');
+
+var _map2 = _interopRequireDefault(_map);
+
+var _wrapAsync = require('./internal/wrapAsync');
+
+var _wrapAsync2 = _interopRequireDefault(_wrapAsync);
+
+function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
+
+/**
+ * Sorts a list by the results of running each `coll` value through an async
+ * `iteratee`.
+ *
+ * @name sortBy
+ * @static
+ * @memberOf module:Collections
+ * @method
+ * @category Collection
+ * @param {Array|Iterable|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 a value to use as the sort criteria as
+ * its `result`.
+ * Invoked with (item, callback).
+ * @param {Function} callback - A callback which is called after all the
+ * `iteratee` functions have finished, or an error occurs. Results is the items
+ * from the original `coll` sorted by the values returned by the `iteratee`
+ * calls. Invoked with (err, results).
+ * @example
+ *
+ * async.sortBy(['file1','file2','file3'], function(file, callback) {
+ *     fs.stat(file, function(err, stats) {
+ *         callback(err, stats.mtime);
+ *     });
+ * }, function(err, results) {
+ *     // results is now the original array of files sorted by
+ *     // modified date
+ * });
+ *
+ * // By modifying the callback parameter the
+ * // sorting order can be influenced:
+ *
+ * // ascending order
+ * async.sortBy([1,9,3,5], function(x, callback) {
+ *     callback(null, x);
+ * }, function(err,result) {
+ *     // result callback
+ * });
+ *
+ * // descending order
+ * async.sortBy([1,9,3,5], function(x, callback) {
+ *     callback(null, x*-1);    //<- x*-1 instead of x, turns the order around
+ * }, function(err,result) {
+ *     // result callback
+ * });
+ */
+function sortBy(coll, iteratee, callback) {
+    var _iteratee = (0, _wrapAsync2.default)(iteratee);
+    (0, _map2.default)(coll, function (x, callback) {
+        _iteratee(x, function (err, criteria) {
+            if (err) return callback(err);
+            callback(null, { value: x, criteria: criteria });
+        });
+    }, function (err, results) {
+        if (err) return callback(err);
+        callback(null, (0, _arrayMap2.default)(results.sort(comparator), (0, _baseProperty2.default)('value')));
+    });
+
+    function comparator(left, right) {
+        var a = left.criteria,
+            b = right.criteria;
+        return a < b ? -1 : a > b ? 1 : 0;
+    }
+}
+module.exports = exports['default'];