用js给TextBox在光标位置插入一段文本

 var range;
                        objText.focus();
                        range = document.selection.createRange();
                        range.moveStart("character", -1);
                        range.select();
                        if(range.text.length == 0)
                        {
                            objText.value = objText.value + objList.value;
                        }
                        else
                        {
                            range.text = range.text + objList.value;
                        }
                        objText.focus();