Calling the JSON Service with AJAX

A wwCallbackHandler derived service is essentially a REST endpoint and you can call it in a number of different ways:

wwCallbackMethod Style
This is the format that's used by the wwMethodCallback control and the wwCallbackMethod client class. It uses POST parameters to push parameters to the server and it's fully automated. This is the easiest way to call a service especially if you use the Proxy features of the wwCallbackMethod class.
Example (using only client wwCallbackMethod class in wwScriptLibrary.js):
```
var Callback = new wwCallbackMethod();
Callback.serverUrl = "ClientCallbacks.ashx";  

// *** parameters passed as values in second parm as array
Callback.callMethod("GetCustomer",[10],
                    CustomerList_Callback,OnError);
```
If you use the wwMethodCallback control this code reduces to a single line:
```
Proxy.GetCustomer(10,CustomerList_Callback,OnError);
```
POST with raw POST buffer
Call the handler with a querystring value of Method=MethodName and simply pass any POST data. The server method you are calling should accept no parameters and can then use Request.Form to read any POST data and use it as input. This mechanism works well if you're using generic AJAX clients like jQuery to call your service.
Example (using wwScriptLibrary.js):
```
ajaxJson("ClientCallbacks.ashx?Method=CallbackWithPost",
         "Name=Rick&Date=01/10/2008&Value=10",                 
         function(result) {alert("Message from Server:\r\n" + result) },
         function(error) { alert(error.message); }, true );
```
POST with JSON string
Call the handler with a querystring of Method=MethodName, set the content type to application/json and pass a POST buffer that contains a JSON encoded value or object. The JSON value is parsed into a .NET object and calls your specified method with a single parameter passing this deserialized JSON object/value.
Example (using wwScriptLibrary.js):
```
ajaxJson("ClientCallbacks.ashx?Method=TestMethod2",
         { Name:"Rick", Date: new Date(), Value:10 }, 
         function(result) {alert("Message from Server:\r\n" + result) },
         function(error) { alert(error.message); } );
```

These examples all use wwScriptLibrary, but that's purely optional. You can use any AJAX library that you like for any of the mechanisms although the first option is probably useful only if you use wwMethodCallback.

Use with jQuery

The following is an example of using jQuery to call a handler:

Passing a raw POST buffer:

$.ajax( {
          url: "ClientCallbacks.ashx?Method=CallbackWithPost",                  
          data: { Name: "Rick", Date: new Date(), Value: 20 },
          processData: true,  // turn input into querystring style values
          dataType: "json",   // result data type 
          type: "POST",
          success: function(result) { alert("Message from Server:\r\n" + result.toLocaleString() ); },
          error: function( xhr, message, ex) { alert("Ajax Error: " + message); }
        }
      );

This code uses an object that is parsed by jQuery.ajax into a raw POST buffer (processData=true which converts a map into POST variables).

Passing a JSON string (note the data must be a JSON string not an object/map!):

// *** Object to serialize
var person = {Name:"Rick",Address:"32 Kaiea",Entered: new Date()};

// *** use wwScriptLibrary's embedded JSON based on Crockford's with mods
// *** you can use whatever mechanism you choose to generate JSON however
// *** although we recommend you use wwScriptLibrary because it's most compatible
// *** with what the server expects.
var jsonData = JSON.serialize( person );

$.ajax( {
          url: "ClientCallbacks.ashx?Method=TestDate",
          contentType: "application/json",
          data: jsonData,
          processData: false,  // treat as json
          dataType: "json",
          type: "POST",
          success: function(result) { alert("Message from Server:\r\n" + result.toLocaleString() ); },
          error: function( xhr, message, ex) { alert("Ajax Error: " + message); }
        }
      );

In this code the data sent is a JSON string. Here I use wwScriptLibrary and its JSON.serialize() function to convert and object into a JSON string that is then passed as a parameter, but you can use whatever mechanism or library you choose to arrive at a JSON string.