Ajax sending a POST request with json

ajax-json.js

$.ajax({
        url: "Service/request",
        async: false,
        type: "POST",
        dataType: "json",
        contentType: "application/json",
        data: JSON.stringify(obj),
        cache: false,
        success: function (data) {
            alert(data);
        },
        error: function (jqXHR, textStatus, errorThrown) {
            alert(textStatus);
        }
});