Javascript限制文本字数的实现代码

<script language="javascript">
/* 
 value: 值； 
 byteLength：数据库字节长度 
 title：字段中文名称 
 attribute：属性名称  --www.jb200.com
 使用方法说明：
添加
1、onkeyup="limitLength(this.value,100,'名称','name')" 
2、id="name" 或【struts标签】styleId="name" 
id名称和 attribute属性名称要一样 

例子：<textarea  name="explain" id="explain" onkeyup="limitLength(value,5,'语义说明','explain')" >  
或
<input type="text"   name="explain"  id="explain" onkeyup="limitLength(value,5,'语义说明','explain')" > 
*/ 
function limitLength(value, byteLength, title, attribute) { 
       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(title + "最大输入" + byteLength + "个字节（相当于"+byteLength /2+"个汉字）！");
   document.getElementById(attribute).value = limitvalue; 
   return; 
}
</script>