Ajax值显示错误

I am using display result(form and custom value(like Json)) ajax. My code:

var data = $("#userForm").serialize() + "&jsonval=" + {"name":"John Doe"}
                    $.ajax({
                    datatype : "json",
                    type: 'POST',
                    url: 'all.php',
                    data: data,
                    })

My Result:

  [firstname] => frtr
    [lastname] => dfgfdg
    [email] => praneshkanna@gmail.com
    [num] => 2323232323
    [num1] => 2342
    [num2] => 2342
    [num3] => 2432
    [submit] => Submit
    [jsonval] => [object Object]

Jsonval -display result [object Object].plz help with display result "John Doe".

Thanks for your feature help and correct my fault.

var obj = {"name":"John Doe"};   
var data = $("#userForm").serialize() + "&jsonval=" + obj.name;