Route:

RouteTable.Routes.MapHttpRoute(name:="DefaultApi", routeTemplate:="api/{controller}/{id}", defaults:=New With {Key
    .id = System.Web.Http.RouteParameter.[Optional]
})

Ajax:

     $.ajax({
                     type: "GET",
                     url: "http://localhost:xxxx/api/xxx/",
                     contentType: "json",
                     dataType: "json",
                     success: function (data) {
                         ...
                         });
                     },
                     error: function (xhr) {
                         alert(xhr.responseText);
                     }
            });