<html>
<head>
<title> new document </title>
<script language="javascript">
</script>
</head>
<body onload="sel()">
<input type="text" name="t1" id="t1" onkeyup="document.getElementById('t2').value=this.value.length" maxlength="5">
<input type="text" name="t2" id="t2">(only 5)
</body>
</html>
http://blog.csdn.net/hztgcl1986/archive/2007/12/04/1915858.aspx
捡了芝麻丢了西瓜，
textarea会损失undo功能，让人难以接受.-----
建议：
textarea的长度校验放在textarea的onblur或form的onsubmit里校验，
以下函数仅供参考：
代码来自JKValidation
http://download.csdn.net/source/276201
/**
*checkMaxLength.
*/
function checkMaxLength(textareaObj,maxLength)
{
if(maxLength == null) maxLength=textareaObj.getAttribute("maxLength");
if(maxLength == null) maxLength=1024;
var currentLength = textareaObj.value.length;
if (currentLength > maxLength) {
alert("The length of your input ("+currentLength+") is larger than maxLength ("+maxLength+") .");
if(textareaObj.createTextRange){
var textRange=textareaObj.createTextRange();
var enterMatch=textareaObj.value.substr(0,maxLength).match(/\n/ig);
var enterNum=0;
if(enterMatch) enterNum=enterMatch.length
textRange.moveStart('character',maxLength-enterNum);
textRange.select();
}
else {
textareaObj.focus();
textareaObj.setSelectionRange(maxLength, currentLength);
}
window.latestValidateObj=textareaObj;
setTimeout("window.latestValidateObj.focus();",0);
return false;
}
return true;
}