jquery how to deserialize json data

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jQuery

Hai I am using the autocomplete box in query _ hear I am getting the data from webmethod in json data now jquery how to deserialize Jason object and bind the TextBox below is my code

$(document).ready(function () {
            debugger;
            $(".autosuggest").autocomplete({
                source: function (request, response) {
                    $.ajax({
                        type: "POST",
                        contentType: "application/json; charset=utf-8",
                        url: "Saleorder.aspx/GetAutoCompleteData",
                        data: "{'username':'" + document.getElementById('pagebody_txtSearch').value + "'}",
                        dataType: "json",
                        success: function (data) {
                            debugger
                            response(data.d);
                        },
                        error: function (result) {
                            alert("Error");
                        }
                    });
                },
                select: function (event, ui) {
                    $.ajax({
                        type: "POST",
                        contentType: "application/json; charset=utf-8",
                        url: "Saleorder.aspx/GetSelectedValue",
                        data: "{'username':'" + ui.item.value + "'}",
                        dataType: "json",
                        success: function (data) {
                            debugger
                            var obj = jQuery.parseJSON(data);
                            alert(obj);
                            //   the alert (obj) is null value . How to bind the value to text box                         
                            $("#<%=txtDeliveryDate.ClientID %>").val(data.d.ItemCode)
                        },
                        error: function (result) {
                            alert("Error");
                        }
                    });
                }
            });
        });