move concurrency arg position in auto (#637)

3 files changed, 10 insertions, 6 deletions

diff --git a/README.md b/README.md
index 293e678..2631add 100644
--- a/README.md
+++ b/README.md
@@ -1256,7 +1256,7 @@ cargo.push({name: 'baz'}, function (err) {
 ---------------------------------------
 
 <a name="auto" />
-### auto(tasks, [callback], [concurrency])
+### auto(tasks, [concurrency], [callback])
 
 Determines the best order for running the functions 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.
 
@@ -1302,13 +1302,12 @@ __Arguments__
   called when finished, passing an `error` (which can be `null`) and the result of
   the function's execution, and (2) a `results` object, containing the results of
   the previously executed functions.
+* `concurrency` - An optional `integer` for determining the maximum number of tasks that can be run in parallel. By default, as many as possible.
 * `callback(err, results)` - 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.
-* `concurrency` - An `integer` for determining the maximum number of tasks that
-  can be run in parallel. By default, as many as possible.
 
 
 __Example__
diff --git a/lib/async.js b/lib/async.js
index 644dccb..beb1372 100644
--- a/lib/async.js
+++ b/lib/async.js
@@ -509,7 +509,12 @@
         }
     };
 
-    async.auto = function (tasks, callback, concurrency) {
+    async.auto = function (tasks, concurrency, callback) {
+        if (!callback) {
+            // concurrency is optional, shift the args.
+            callback = concurrency;
+            concurrency = null;
+        }
         callback = _once(callback || noop);
         var keys = _keys(tasks);
         var remainingTasks = keys.length;
diff --git a/test/test-async.js b/test/test-async.js
index 34fabaf..ac72fed 100755
--- a/test/test-async.js
+++ b/test/test-async.js
@@ -352,12 +352,12 @@ exports['auto concurrency'] = function (test) {
         task4: ['task1', 'task2', makeCallback('task4')],
         task5: ['task2', makeCallback('task5')],
         task6: ['task2', makeCallback('task6')]
-    }, function(err, results){
+    }, concurrency, function(err, results){
         Object.keys(results).forEach(function(taskName) {
             test.ok(results[taskName].length <= concurrency);
         });
         test.done();
-    }, concurrency);
+    });
 };
 
 exports['auto petrify'] = function (test) {