ajaxCFC and 0 Return Values

Posted At : March 7, 2007 5:17 PM | Posted By : Nathan Mische
Related Categories: ColdFusion,JavaScript

I've been using ajaxCFC on a project at work and I ran into an issue today which I thought I'd share.

Say you have a simple ajax component:

<cfcomponent extends="ajax">   

   <cffunction name="echo" output="no" access="private">

      <cfargument name="num" required="yes" type="numeric">      

      <cfreturn val(arguments.num) />

   </cffunction>

</cfcomponent>

You set up a call to this method like so:

<html>

<head>

   <title>echo number example</title>

   <script type='text/javascript'>

      _ajaxConfig = {   '_cfscriptLocation':'echoNumber.cfc',

                  '_jsscriptFolder':'../js',

                  'debug':true};

   </script>

   <script type='text/javascript' src='../js/ajax.js'></script>

   <script type="text/javascript">

      function doEcho()   {

         DWREngine._execute(_ajaxConfig._cfscriptLocation, null, 'echo', 0, doEchoResult);

      }



      // call back function
      function doEchoResult (r) {

         alert(r);

      }



   </script>

</head>

<body onload="doEcho();">

   <p>Nothing Happens!</p>

</body>

</html>

This results in the following response:

HTTP/1.1 200 OK

Connection: close

Date: Wed, 07 Mar 2007 18:14:36 GMT

Server: Microsoft-IIS/6.0

Content-Type: text/html; charset=UTF-8





_3952_1173291282046 = 0;



DWREngine._handleResponse('3952_1173291282046', _3952_1173291282046);

This looks fine, however the callback function doEchoResult never gets called. The reason is the DWREngine._handleRespone function checks the result before calling the callback function.

DWREngine._handleResponse = function(id, reply) {

  ...

  if (handlers && reply) {

    ...

    try {

      if (handlers.callback) handlers.callback(reply);

    }

    catch (ex) {

      DWREngine._handleMetaDataError(handlers, ex);

    }

  }

  ...

}

The problem here is that the reply argument (the _3952_1173291282046 variable in this example) will be evaluated to false so the callback never gets called.

Now the DWREngine code could be updated to handle this by checking that reply != null, however I'm a little leary of changing core framework code. Plus I haven't really taken a good look at the DWREngine code to know if this will cause any other issues. In the end I decided to modify my component function to work around this issue rather than change the core ajaxCFC files. I've submitted a bug to the RIAForge project, so this may get fixed in a future release. (Or maybe Rob Gonda will chime in and tell me I'm doing things all wrong. :)