输入框限制输入30字节，超过的去掉并提示。该如何实现？

function leng()
        {
            var len = $("#ts").val();
            var total = 0;
            for(i = 0; i < len.length; i++)
            {
                if(len[i].match(/[^\x00-\xff]/ig) != null)
                {
                    total = total + 2;
                }
                else
                {
                    total = total + 1;
                }
                if (total > 30)
                {
                    $("#ts").val(len.substring(0,i));
                    break;
                }
            }
        }
?