datatables empty

HTML

<script src="http://cdn.datatables.net/1.10.5/js/jquery.dataTables.min.js"></script>
<link rel="stylesheet" href="http://cdn.datatables.net/1.10.5/css/jquery.dataTables.css">
<ul>
    <li><a href="#" id="currentTasks">"current"</a></li>
    <li><a href="#" id="archiveTasks">"archive"</a></li>
 </ul>
<table id="baseTasks">
    <thead>
    <tr>
      <th class="now-task">name</th>
      <th class="now-curat">schoolClass</th>
      <th class="now-class">complexity</th>
      <th class="now-compl">author</th>
    </tr>
    </thead>

  </table>

JavaScript

var tasks = [];

function getTask(url){
    //in reality, ajax request here
    if(url == 1)
        tasks = [];
    else
        tasks = [{name:"task1",  schoolClass:"1",  complexity:"1",  author:"Smith"},
                     {name:"task2",  schoolClass:"2",  complexity:"2",  author:"Jons"}]      
}

getTask(2);

var searchTable = $('#baseTasks').dataTable({
        bFilter: false, bInfo: false, "bLengthChange": false,
        scrollY:"600px",scrollCollapse: true, paging:false,
        "aaData": tasks,
        "aoColumns": [
         { "mData": "name"
         },{"mData": "schoolClass"
         },{"mData": "complexity"
         },{"mData": "author"
    }]
});

$('#archiveTasks').click(function () {
    searchTable.fnClearTable();
    getTask(1);
    searchTable.fnAddData(tasks);   
});

$('#currentTasks').click(function () {
    searchTable.fnClearTable();
    getTask(2);
    searchTable.fnAddData(tasks);
});