js form表单input框限制20个字符，10个汉字代码实例

直接粘贴到html文件便可看到效果

<!DOCTYPE html>
<html>
 <head>
  <meta charset="utf-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1" />
  <script src="https://cdn.bootcss.com/jquery/3.3.1/jquery.min.js"></script>
  <script>
   // 这是第一种最寻常的方法
   //定义一个函数
   function checkField(value, byteLength, attribute) {
    // value是input框的值,byteLength是需求限制的字符，attribute是input的id名
    var newvalue = value.replace(/[^\x00-\xff]/g, "**");
    var length = newvalue.length;
    //当填写的字节数小于设置的字节数
    if (length * 1 <= byteLength * 1) {
     return;
    }
    var limitDate = newvalue.substr(0, byteLength);
    var count = 0;
    var limitvalue = "";
    for (var i = 0; i < limitDate.length; i++) {
     var flat = limitDate.substr(i, 1);
     if (flat == "*") {
      count++;
     }
    }
    var size = 0;
    var istar = newvalue.substr(byteLength * 1 - 1, 1); //校验点是否为“×”
    //if 基点是×; 判断在基点内有×为偶数还是奇数
    if (count % 2 == 0) {
     //当为偶数时
     size = count / 2 + (byteLength * 1 - count);
     limitvalue = value.substr(0, size);
    } else {
     //当为奇数时
     size = (count - 1) / 2 + (byteLength * 1 - count);
     limitvalue = value.substr(0, size);
    }
    alert(
     "最大输入" +
      byteLength +
      "个字节（相当于" +
      byteLength / 2 +
      "个汉字）！"
    );
    document.getElementById(attribute).value = limitvalue;
    return;
   }
  </script>
 </head>
 <body>
  <div class="wrap">
   <form>
    <table class="list-style">
     <tr>
      <td style="width:15%;text-align:right;">职业：</td>
      <td>
       <input id="profession" type="text" "checkField(this.value,20,'profession')" class="textBox length-middle" name="profession"/>
       <input id="interest" type="text" "checkField(this.value,100,'interest')" class="textBox length-middle" name="interest"/>
       <input id="address" "checkField(this.value,40,'address')" type="text" class="textBox length-middle" name="address" />
      </td>
     </tr>
    </table>

    <div style="margin:20px 0 0 300px">
     <button
      type="reset"
      style="width:60px;height:30px;margin-right:40px"
      "refresh()"
     >
      重置
     </button>
     <button
      type="submit"
      style="width:60px;height:30px"
      "return checkNull()"
     >
      提交
     </button>
    </div>
   </form>
  </div>
 </body>
</html>

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