important bug fix, only default options if none provided, phetsims/ru…

…therford-scattering#128
phetsims · Oct 26, 2017 · fd6191f · fd6191f
1 parent b043daf
commit fd6191f
Showing 1 changed file with 2 additions and 2 deletions.
diff --git a/js/NumberControl.js b/js/NumberControl.js
@@ -287,8 +287,8 @@ define( function( require ) {
       'Use general callbacks like "startCallback" or specific callbacks like "sliderStartCallback" but not both.' );
 
     // Set here so that we can validate above based on falsey.
-    options.startCallback = function() {};
-    options.endCallback = function() {};
+    options.startCallback = options.startCallback || function() {};
+    options.endCallback = options.endCallback || function() {};
   }
 
   sceneryPhet.register( 'NumberControl', NumberControl );