<html>
<head runat="server">
<title></title>
<script type="text/javascript">
var maxstrlen = 160;
function Q(s) { return document.getElementById(s); }
function checkWord(c) {
len = maxstrlen;
var str = c.value;
myLen = getStrleng(str);
var wck = Q("wordCheck");
if (myLen > len * 2) {
c.value = str.substring(0, i + 1);
}
else {
wck.innerHTML = Math.floor((len * 2 - myLen) / 2);
}
}
function getStrleng(str) {
myLen = 0;
i = 0;
for (; (i < str.length) && (myLen <= maxstrlen * 2); i++) {
if (str.charCodeAt(i) > 0 && str.charCodeAt(i) < 128)
myLen++;
else
myLen += 2;
}
return myLen;
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div style="font-size: 16px">
控制输入框字符输入，计算输入字符总数,显示剩余字数;<br>
一个英文字符算一个字符，一个中文字符算两个字符计算。
</div>
<div>
<textarea onkeyup="javascript:checkWord(this);" onmousedown="javascript:checkWord(this);"
name="content" style="overflow-y: scroll"></textarea>
</div>
<div>
还可以输入<span style="font-family: Georgia; font-size: 26px;" id="wordCheck">160</span>个字符
</div>
</form>
</body>
</html>
原文：http://www.cnblogs.com/zhoumeng780/p/4891936.html