append from cursor javascript

Click Here to Insert

A1 A2 A3

 function IFAdd() {
                ifobj = window.frames.iframe1;
                var e = document.getElementById("DropDownList1");
                bookmark = e.options[e.selectedIndex].value;
               // bookmark = document.getElementById('HiddenField1').value;
                // this hidden field hv valueselected value  from drop down 
                //txt = ifobj.document.createTextNode(bookmark);
              // ifobj.contentEditable = true;            
              // ifobj.document.getElementsByTagName('BODY')[0].contentEditable = true;
               
              insertAtCaret('textareaid',bookmark);
                return false;
            }

function insertAtCaret(areaId,text) {
    var txtarea = document.getElementById(areaId);
    var scrollPos = txtarea.scrollTop;
    var strPos = 0;
    var br = ((txtarea.selectionStart || txtarea.selectionStart == '0') ? 
        "ff" : (document.selection ? "ie" : false ) );
    if (br == "ie") { 
        txtarea.focus();
        var range = document.selection.createRange();
        range.moveStart ('character', -txtarea.value.length);
        strPos = range.text.length;
    }
    else if (br == "ff") strPos = txtarea.selectionStart;

    var front = (txtarea.value).substring(0,strPos);  
    var back = (txtarea.value).substring(strPos,txtarea.value.length); 
    txtarea.value=front+text+back;
    strPos = strPos + text.length;
    if (br == "ie") { 
        txtarea.focus();
        var range = document.selection.createRange();
        range.moveStart ('character', -txtarea.value.length);
        range.moveStart ('character', strPos);
        range.moveEnd ('character', 0);
        range.select();
    }
    else if (br == "ff") {
        txtarea.selectionStart = strPos;
        txtarea.selectionEnd = strPos;
        txtarea.focus();
    }
    txtarea.scrollTop = scrollPos;
}