jQuery Datatables动态构建列数据选项

Question

遇到数据表列问题。我试图动态创建列数据选项但不起作用。如果我对列进行硬编码就可以了。

这最终将使用Ajax作为数据，我永远不会知道返回的列或数据，并且必须是完全动态的。

Getting Error: 
Timestamp: 4/6/2015 1:00:27 PM
Error: TypeError: invalid 'in' operand a
Source File: http://52.4.158.201/js/jquery-2.1.1.min.js
Line: 2

HTML

<table id="example2">
    <thead>
        <tr></tr>
    </thead>
    <tbody></tbody>
</table>

Javascript

    $(document).ready(function()
{
    var dataTest = '{"header": ["Name","Position","Office","Age","Start_date","Salary"],"staff": [{"name":"Tiger Nixon","position":"System Architect","office":"Edinburgh","age":61,"Start_date":"2011/04/25","salary":"$320,800"},{"name":"Garrett Winters","position":"Accountant","office":"Tokyo","age":63,"Start_date":"2011/07/25","salary":"$170,750"},{"name":"Ashton Cox","position":"Junior Technical Author","office":"San Francisco","age":66,"Start_date":"2009/01/12","salary":"$86,000"}]}';
    var obj = JSON.parse(dataTest);

    for(var i = 0; i < obj.header.length; i++)
    {
        $('#example2 thead tr').append('<th>' + obj.header[i] + '</th>');
    }

    var dtColumns = '';
    var c = 0;

    for (var prop in obj.staff)
    {
        if(c == 0)
        {
            for(var key in obj.staff[prop])
            {
                 dtColumns = dtColumns + '{"data":"'+ key +'"},';
            }
        }
        else
        {
            break;
        }

        c++;
    }

    dtColumns = dtColumns.replace(/,+$/,'');

    //console.log(dtColumns);

    $('#example2').DataTable({
        data: obj.staff,
        columns: [dtColumns]
    });

    /*
     * WORKS
     */
    /*
    var table2 = $('#example2').DataTable({
        data: obj.staff,
        columns: [
                    {'data':'name'},
                    {'data':'position'},
                    {'data':'office'},
                    {'data':'age'},
                    {'data':'Start_date'},
                    {'data':'salary'}
        ]
    });
    */

    //table2.rows.add(obj.staff).draw();
});