Question

I created a simple AJAX-enabled WCF service based on the MSDN tutorial

[ServiceContract(Namespace = "AjaxWcf")]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
public class AjaxWcf
{

    [OperationContract]
    public string AssessString(string input)
    {
        if (input.Contains("1"))
            return "true";

        return "false";
    }

which totally works when i generate the js proxy and use ASP.NET AJAX library to call.

However when i switch over to jQuery to make the ajax() call, it get an [object XMLHttpRequest] error

$.ajax({ url: "AjaxWcf.svc/AjaxWcf/AssessString",
    type: "POST",
    dataType: "text",
    processData: false,
    data: { input: inputValue },
    error: 
    function (msg) { $("#serviceResponse").html(msg.toString()); },
    success: function (response)
    { $("#serviceResponse").html(response); }
    });

I have read around about what to make of that error and a suggestion to alter the error delegate to peek further into the problem

function (xmlHttpRequest, textStatus, errorThrown) {
    if (xmlHttpRequest.readyState == 0 || xmlHttpRequest.status == 0)
        return;  // it's not really an error 
    else
    $("#serviceResponse").html(errorThrown);
    },

which then caused IE to to choke

Microsoft JScript runtime error: Could not complete the operation due to error c00c023f.

Apparently that is an IE9-only problem, but testing this in Google Chrome still did not yield any web service invocation (breakpoint never gets hit). And if i use back to old error delegate, the same [object XMLHttpRequest] problem. I am kind of surprised at the lack of materials discussing a simple POST call with jQuery to WCF service, and wonder what is missing?

Note: this is using jQuery 1.4.1, but as far as i’ve seen using 1.7.1 still did not call the WCF service.

Answer 1

For reasons not fully understood at this point, it appears that jQuery AJAX to WCF service should be carried out using JSON data type.

$.ajax({ url: "AjaxWcf.svc/AssessString",
    type: "POST",
    dataType: "json",
    contentType: "application/json",
    processData: false,
    data: postData,
    error: function (msg)
    { alert(msg.responseText); },
    success: function (response)
    { $("#serviceResponse").html(response.d); }
});

This way the browser is able to make the request out without hitting errors and reaching the service endpoint.