ASP.NET calling a web service from javascript

Calling a web service from javascript should be a very easy task.
Especially if you are using prototype or jquery in your project.

The other day I spent to much time trying to call a WebService using Prototype js library so I decided to post the code here in case anyone else encounter the same problem.
Server side code:
            [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
            public class WebService : System.Web.Services.WebService
                public string HelloWorld(string testParam)
                    return testParam;
Prototype syntax:
            new Ajax.Request('WebServices/WebService.asmx/HelloWorld',
                postBody: "{testParam:'hello'}",
                method: 'post',
                contentType: 'application/json; charset=utf-8',
                onSuccess: function(transport) {
                onFailure: function(transport) {
JQuery syntax:
                    type: "POST",
                    url: "WebServices/WebService.asmx/HelloWorld",
                    data: "{testParam:'hello'}",
                    contentType: "application/json; charset=utf-8",
                    dataType: "json",
                    success: function(result){
That’s it.
Hope it help someone out
Happy coding!