JavaScript实现字符串长度校验：中文字符计为2，英文数字计为1

<html>
<head>
  <title>js判断输入字符串长度（汉字算两个字符，字母数字算一个）</title>
  <style type="text/css">
    .pbt {
      margin-bottom: 10px;
    }

    .ie6 .pbt .ftid a, .ie7 .pbt .ftid a {
      margin-top: 1px;
    }

    .cl:after {
      clear: both;
      content: ".";
      display: block;
      height: 0;
      visibility: hidden;
    }
  </style>
  <script type="text/javascript">
    //获取字符串长度（汉字算两个字符，字母数字算一个）
    function getByteLen(val) {
      var len = 0;
      for (var i = 0; i < val.length; i++) {
        var a = val.charAt(i);
        if (a.match(/[^\x00-\xff]/ig) != null) {
          len += 2;
        }
        else {
          len += 1;
        }
      }
      return len;
    }
    // 只要键盘一抬起就验证编辑框中的文字长度，最大字符长度可以根据需要设定
    function checkLength(obj) {
      var maxChars = 80;//最多字符数   
      var curr = maxChars - getByteLen(obj.value);
      if (curr > 0) {
        document.getElementById("checklen").innerHTML = curr.toString();
      } else {
        document.getElementById("checklen").innerHTML = '0';
        document.getElementById("subject").readOnly = true;
      }
    }
  </script>
</head>
<body>
  <div class="pbt cl">
    <textarea id="subject" maxlength="80" onkeyup="checkLength(this)" accesskey="1" tabindex="11"></textarea>
    <span id="subjectchk">还可输入
    <strong id="checklen" style="color: #FF0000">80</strong>
      个字符
    </span>
    <span id="postNameRule" class="spn_flag_1" style="display: none"></span>
  </div>
</body>
</html>