JSONP with jQuery and ASP.NET

JSONP allows you to execute something similar to AJAX, across domains without worrying about whether the request is across domains, or any special CORS configuration.

It’s not generally a huge deal to set up CORS, but JSONP is guaranteed to work in all browsers and servers without any special handling.

function go() {
    jQuery.ajax({
        // url: "/Home/DoSomething", // Regular MVC
        // url: "/Handler1.ashx", // WebForms
        data: {xyz:"World"},
        dataType: "jsonp",
        type: "get"
    }).done(function (result) {
        console.log(result);
    });
}

// Regular MVC - no special filters, return types, etc. 
public ActionResult DoSomething(string xyz) 
{
    Response.ContentType = "application/json";
    var foo = new { FirstName = "John", LastName = "Doe", Message = "Hello " + xyz };
    Response.Write(string.Format("{0}({1});", Request["callback"], JsonConvert.SerializeObject(foo)));
    return null;
}
 
// WebForms
public class Handler1 : IHttpHandler 
{
    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "application/json";
        var foo = new { FirstName = "John", LastName = "Doe", Message = "Hello " + context.Request["xyz"] };
        context.Response.Write(string.Format("{0}({1});", context.Request["callback"], JsonConvert.SerializeObject(foo)));
    }
 
    public bool IsReusable { get { return false; } }
}