JS：

//多行文本输入框剩余字数计算

        function checkMaxInput(obj, maxLen) {

            if (obj == null || obj == undefined || obj == "") {

                return;

            }

          /*if (maxLen == null || maxLen == undefined || maxLen == "") {

                maxLen = 250;

            }*/

           /* var strResult;

            var $obj = $(obj);

            var newid = $obj.attr("id") + 'msg';*/

            $('#number').show();

            if (obj.value.length > maxLen) {    //如果输入的字数超过了限制

                obj.value = obj.value.substring(0, maxLen); //就去掉多余的字

                document.getElementById("msg").innerHTML ="剩"+(maxLen - obj.value.length).toString()+"字";

                //strResult = '<a><span id="' + newid + '" class=\'Max_msg\' ><br/>剩(' + (maxLen - obj.value.length) + ')字</span></a>'; //计算并显示剩余字数

            }

            else {

                //strResult = '<a><span id="' + newid + '" class=\'Max_msg\' ><br/>剩(' + (maxLen - obj.value.length) + ')字</span></a>'; //计算并显示剩余字数

                document.getElementById("msg").innerHTML =(maxLen - obj.value.length).toString();

            }

           /* var $msg = $("#" + newid);

            if ($msg.length == 0) {

                $obj.after(strResult);

            }

            else {

                $msg.html(strResult);

            }*/

        }

        //清空剩除字数提醒信息

        function resetMaxmsg() {

            $('#number').hide();

        }

<textarea name="remarks" style="background-color:#CDFF9A;height:285px;width:165px;resize:none;" onkeydown="checkMaxInput(this,120)"

            onkeyup="checkMaxInput(this,120)" onfocus="checkMaxInput(this,120)" onblur="checkMaxInput(this,120);resetMaxmsg()"></textarea>

<div style="position:absolute;top:200px;left:250px"><a style="display:none" id="number">剩（<span id="msg">120</span>）字</a></div>

效果：

aaarticlea/png;base64,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" alt="" />