// вставка bbcode
function insertBBCode(taObj, bbTag, promptText) {
    if (!taObj) return false;
    var caretPos = 0;
    var start = 0;
    var end = 0;
    var selText;
    var openBB = "";
    if (promptText) {
        var usText = prompt(promptText, '');
        if (usText) openBB = "["+bbTag+"="+usText+"]";
        else          openBB = "["+bbTag+"]";
    }
    else {openBB = "["+bbTag+"]";}
    var closeBB = "[/"+bbTag+"]";
    taObj.focus();
    if (document.getSelection || window.getSelection)  {
        start = taObj.selectionStart;
        end = taObj.selectionEnd;
    }
    else if (document.selection) {
        var sel = document.selection.createRange();
        var clone = sel.duplicate();
        sel.collapse(true);
        clone.moveToElementText(taObj);
        clone.setEndPoint("EndToEnd", sel);
        start = clone.text.length;
        sel = document.selection.createRange();
        clone = sel.duplicate();
        sel.collapse(false);
        clone.moveToElementText(taObj);
        clone.setEndPoint("EndToEnd", sel);
        end = clone.text.length;
    }
    if (start === end) {
        var str = taObj.value;
        taObj.value = str.substring(0, start)+openBB+closeBB+str.substr(start);
        var nPos = start+openBB.length;
        if (taObj.createTextRange) {
            var caret = taObj.createTextRange();
            caret.collapse();
            caret.moveStart("character", nPos);
            caret.select();
        }
        else if(window.getSelection) {
            taObj.setSelectionRange(nPos, nPos);
            taObj.focus();
        }
    }
    else if (start < end) {
        var str = taObj.value;
        selText = str.substring(start, end);
        taObj.value = str.substring(0, start)+openBB+selText+closeBB+str.substr(end);
    }
}
var textarea = null;
window.onload = function() {
    textarea = document.getElementById('text'); // Вместо 'mytextarea' введите id вашего элемента textarea
}