move concurrency arg position in auto (#637)

1 files changed, 6 insertions, 1 deletions

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;