限制textbox或textarea输入字符长度的JS代码

<script language=javascript> 
<!-- String.prototype.len=function(){ 
return this.replace(/[^\x00-\xff]/g,"**").length; 
} 
//Set maxlength for multiline TextBox 
function setMaxLength(object,length) 
{ 
var result = true; 
var controlid = document.selection.createRange().parentElement().id; 
var controlValue = document.selection.createRange().text; 
if (controlid == object.id && controlValue != "") 
{ 
result = true; 
} 
else if (object.value.len() >= length) 
{ 
result = false; 
} 
if (window.event) 
{ 
window.event.returnValue = result; 
return result; 
} 
} 
//Check maxlength for multiline TextBox when paste 
function limitPaste(object,length) 
{ 
var tempLength = 0; 
if(document.selection) 
{ 
if(document.selection.createRange().parentElement().id == object.id) 
{ 
tempLength = document.selection.createRange().text.len(); 
} 
} 
var tempValue = window.clipboardData.getData("Text"); 
tempLength = object.value.len() + tempValue.len() - tempLength; 
if (tempLength > length) 
{ 
tempLength -= length; 
//alert(tempLength); 
//alert(tempValue); 
var tt=""; 
for(var i=0;i<tempValue.len()-tempLength;i++) 
{ 
if(tt.len()<(tempValue.len()-tempLength)) 
tt=tempValue.substr(0,i+1); 
else 
break; 
} 
tempValue=tt; 
window.clipboardData.setData("Text", tempValue); 
} 
window.event.returnValue = true; 
} 
//--> 
</script>

然后设多行的textbox或textarea的2个属性.
onkeypress="javascript:setMaxLength(this,100);" onpaste="limitPaste(this, 100)"
现在好了，可以自动区分中英文了，这个方案不错，供大家分享