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jquery判断字符输入个数(数字英文长度记为1,中文记为2,超过长度自动截

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
 <HEAD>
  <TITLE> New Document </TITLE>
  <script type="text/javascript" src="jquery-1.4.2.min.js"></script>
 </HEAD>

 <BODY>
  
<div> 
<textarea id="txtPrizeNote" runat="server" height="74px" width="480px" maxlength="10" 
style="width: 480px; height: 74px; float: left"></textarea> 
<span style="color: Red;">*</span><br /> 
剩余字数:<span id="showmsg" style="color: red"></span> 
</div> 
 </BODY>
</HTML>

<script type="text/javascript"> 
//返回val的字节长度 
function getByteLen(val) { 
var len = 0; 
for (var i = 0; i < val.length; i++) { 
if (val[i].match(/[^\x00-\xff]/ig) != null) //全角 
len += 2; 
else 
len += 1; 
} 
return len; 
} 
//返回val在规定字节长度max内的值 
function getByteVal(val, max) { 
var returnValue = ''; 
var byteValLen = 0; 
for (var i = 0; i < val.length; i++) { 
if (val[i].match(/[^\x00-\xff]/ig) != null) 
byteValLen += 2; 
else 
byteValLen += 1; 
if (byteValLen > max) 
break; 
returnValue += val[i]; 
} 
return returnValue; 
} 
$(function() { 
var _area = $('textarea#txtPrizeNote'); 
var _info = _area.next(); 
var _max = _area.attr('maxlength'); 
var _val; 
_area.bind('keyup change', function() { //绑定keyup和change事件 
if (_info.find('span').size() < 1) {//避免每次弹起都会插入一条提示信息 
_info.append(_max); 
} 
_val = $(this).val(); 
_cur = getByteLen(_val); 
if (_cur == 0) {//当默认值长度为0时,可输入数为默认maxlength值 
_info.text(_max); 
} else if (_cur < _max) {//当默认值小于限制数时,可输入数为max-cur 
_info.text(_max - _cur); 
} else {//当默认值大于等于限制数时 
_info.text(0); 
$(this).val(getByteVal(_val,_max)); //截取指定字节长度内的值 
} 
}); 
}); 
</script> 


引自:http://www.jb51.net/article/25001.htm
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