checking for the existence of a dom object

$("select").change(function(event){
    switch(
        $(this).val()){
            case '0':
            break;
            case '1': case '5': case '6': case '8': case '9': case '10':
                if($("txComments").length > 0){

                }else{
                $('#MainTable').append('<p style="float:left;width:99%" class="dateWidth">Comments:  <br/><textarea id="txComments" name="txComments" class="ui-state-default ui-corner-all" id="rDetails" style="width:100%; height: 120px"></textarea></p>');
                }
                break;
            }
});