<style type="text/css">

        textarea{

            width: 400px;

            height:400px;

            resize: none;

        }

        .limit{

            width: 400px;

            text-align: right;

        }

        #d1{

            margin: 100px;

        }

        input::-webkit-input-placeholder{

            color:red;

        }

        input::-moz-placeholder{   /* Mozilla Firefox 19+ */

            color:red;

        }

        input:-moz-placeholder{    /* Mozilla Firefox 4 to 18 */

            color:red;

        }

        input:-ms-input-placeholder{  /* Internet Explorer 10-11 */

            color:red;

        }

        textarea::-webkit-input-placeholder{

            color:red;

        }

        textarea::-moz-placeholder{   /* Mozilla Firefox 19+ */

            color:red;

        }

        textarea:-moz-placeholder{    /* Mozilla Firefox 4 to 18 */

            color:red;

        }

        textarea:-ms-input-placeholder{  /* Internet Explorer 10-11 */

            color:red;

        }

    </style>

    <div id = "d1">

        <div>

        <input type="text" placeholder='的奇偶为不让你'/>

            <textarea placeholder='减肥的设计费我没如风达'/>

        </div>

        <div class="limit">

            最大可输入

            <span></span>/

        </div>

    </div>

    <script type="text/javascript">

        //先定义计算字符串字数

        function getStrleng(str,max) {

            myLen = ;

            i = ;

            for (; (i < str.length) && (myLen <= max * ); i++) {

                if (str.charCodeAt(i) >  && str.charCodeAt(i) < )           //根据Unicode编码值判断是否汉字

                    myLen++;

                else

                    myLen += ;

            }

            return myLen;

        }

        //定义函数获得DOM元素

        function Q(s){

            return document.querySelector(s);

        }

        //定义函数显示写了几个字

        function checkWord(c) {

            var maxstrlen = ;

            var str = c.value;              //对象的内容

            myLen = getStrleng(str,maxstrlen);   //计算str的字符个数

            var wck = Q(".limit span");

            console.log(wck)

            if(myLen > maxstrlen * ){

                c.value = str.substring(, i - );

            }else{

                wck.innerHTML = Math.floor(myLen / );

            }

        }

        Q('textarea').onkeyup =function(){

            checkWord(this);

        }

    </script>