--- a/common/bindings/spinbuttons.xml
+++ b/common/bindings/spinbuttons.xml
@@ -81,17 +81,17 @@
             eventname = "down";
 
           var evt = document.createEvent("Events");
           evt.initEvent(eventname, true, true);
           var cancel = this.dispatchEvent(evt);
 
           if (this.hasAttribute("on" + eventname)) {
             var fn = new Function("event", this.getAttribute("on" + eventname));
-            if (fn.call(this, event) == false)
+            if (!fn.call(this, event))
               cancel = true;
           }
 
           return !cancel;
         ]]>
       </handler>
 
     </handlers>