=== Introduction === 

Here's a simple recipe that worked for me. It is quite inspired by the [wiki:AjaxDojoFormSub] example―and from [http://www.b-list.org/weblog/2006/07/31/django-tips-simple-ajax-example-part-1 this tutorial]―except that this recipe is using python-cjson to receive JSON-encoded data.

My initial objective was to display validation errors without doing a page-refresh, while using 
JSON for carrying errors (or whatever else you could possibly imagine) back to the client browser. 

=== The server view ===

First thing first, lets write the server view, as its really important to make the forms working 
without the use of Javascript:

{{{
#!python
import cjson
from django.http import HttpResponse
from django.template import loader, Context

def register(request):
    # Register or reports any (new)form-validation errors using JSON.
    form = ExampleForm(request.POST)
    t = loader.get_template('myform.html')
    if not form.is_valid():
       # Return JSON object containing the errors object.
       if xhr:
          return HttpResponse(cjson.encode(form.errors), mimetype='text/javascript')
       else:
          # No JSON here!
          return HttpResponse(t.render(Context(form.errors))
    else:
       # Do something when the form has been validated.
       ...    
}}}

=== The client view ===

Once the server view has been written, the idea is to write down the client UI (or view, 
depending whether you're a purist or not.. ;-)

Quite frankly, that step is straight-forward, and looks pretty-much like writing down 
basic HTML:
{{{
#!text/html
<script type="text/javascript">
    djConfig = {
        isDebug: true,
        debugAtAllCosts: false
    };
</script>
<script type="text/javascript" src="/media/js/dojo/dojo.js"></script>
<script type="text/javascript">
    dojo.require("dojo.event.*");       // sophisticated AOP event handling
    dojo.require("dojo.io.*");          // for Ajax requests
    dojo.require("dojo.json");          // serialization to JSON
</script>
<!-- Here's the client UI script to play with Dojo  -->
<script type="text/javascript" src="/media/js/ajax.js"></script>
}}}   

The {{{djConfig.isDebug}}} parameter is important for debugging, so you should 
consider setting it to "true" when inspecting you're application with Firebug
or something else. 

To avoid loading the Dojo modules twice (for speed), just roll your own Dojo script, 
and then remove the implied ("baked") modules from the list of required modules above.

=== Form validating with dojo.io.bind ===
 
Let's complete our application by writing down the core JS file, 
for doing some-cute-AJAX-related-things-with-Dojo:

ajax.js:
{{{
function myinit() {
    // connect the event with the good handler
    var myButton = dojo.byId("xBtn1");
    dojo.event.connect(myButton, "onclick", "sendForm");
};
function sendForm() {
    var fNode = dojo.byId('xForm')
    var fParms = dojo.io.encodeForm(fNode)
    var myErrorDiv = dojo.byId('errorBox1')
    var bindArgs = {
        url: ".",
        mimetype: 'text/plain',
        method: "post",
        preventCache: true,
        transport: "XMLHTTPTransport",
        postContent: fParms,
        error: function(type, error, http){
               // Handle error here
               alert(error.message)
               if (http.responseText)
                   // Return the raw server response
                   // (useful when debugging)
                   document.write(http.responseText)
               return false
        },
        load: function(type, data, http, kwArgs){
              // Handle "successful" responses here
              var errStr = ''
              if(type == 'load'){
                try {
                 var json = eval( '(' + data + ')' )
                } catch (e) {
                  // not json
                  document.write(data)
                  return false
                }
                for (x in json) 
                    errStr += x + ': ' + json[x] + '<br />'
                myErrorDiv.innerHTML = errStr
              }
         }
    };
    var xmlhttp = dojo.io.bind(bindArgs)
    return xmlhttp
};
dojo.addOnLoad(myinit);
}}}

Notice the absence of the {{{formNode}}} param for {{{postContent}}}, and the presence of {{{dojo.io.encodeForm}}} to parse/encode the form data into a proper format. That is more than sufficient for validating the 
form with a {{{XMLHTTPTransport}}}. However, this approach doesn't work per se with file-uploads. To have file-uploads,
you could however change the {{{transport}}} line to {{{IframeTransport}}}. Here's a link to the [http://dojotoolkit.org/api/?#dojo.io.IframeTransport IframeTransport api]. 

Have fun! That recipe should work in Firefox 2 and Opera 9.10.

=== Limitations/Bugs === 

 * Usability issues: HTML 4.01 vs XHTML 1.0 strict vs No javascript
 * XMLHTTPTransport doesnt support file-uploading.  

=== Notes/Comments/Suggestions === 

Add some notes (or comments!) here. :-)

=== References ===

 * [http://cheeseshop.python.org/pypi/python-cjson/ python-cjson]
 * [http://dojotoolkit.org/ Dojo, the Javascript Toolkit]
 * [http://dojotoolkit.org/api/ Dojo API Reference]
 * [http://www.w3.org/TR/html401/ HTML 4.01 Specification]
 * [http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Reference Core Javascript 1.5 Reference (mozilla)]
 * [http://www.opera.com/docs/specs/opera9/js/ecma/ ECMAScript support in Opera 9]

=== Author ===

Etienne Robillard <erob@cpan.org>