Thx, but I already find a solution for my problem.
Code:
function InsertBBCode() {
if(document.getSelection) {
area_val = area.value.substring(0,area.selectionStart) + first_bb_arr +
area.value.substring(area.selectionStart,area.selectionEnd) +
sec_bb_arr + area.value.substring(area.selectionEnd,area.value.length);
area.value = area_val;
} else {
var selectedText = document.selection.createRange().text;
if(selectedText!='') {
var newText = first_bb_arr + selectedText + sec_bb_arr;
document.selection.createRange().text = newText;
}
}
}