TextArea设置MaxLength的代码（未测试在不同浏览器下的兼容性）

function SetTextAreaMaxLength(controlId,length)
{
// JScript File for TextArea
// Keep user from entering more than maxLength characters
function doKeypress(control,length){
maxLength = length;
value = control.value;
if(maxLength && value.length > maxLength-1){
event.returnValue = false;
maxLength = parseInt(maxLength);
}
}
// Cancel default behavior
function doBeforePaste(control,length){
maxLength = length;
if(maxLength)
{
event.returnValue = false;
}
}
// Cancel default behavior and create a new paste routine
function doPaste(control,length){
maxLength = length;
value = control.value;
if(maxLength){
event.returnValue = false;
maxLength = parseInt(maxLength);
var oTR = control.document.selection.createRange();
var iInsertLength = maxLength - value.length + oTR.text.length;
var sData = window.clipboardData.getData("Text").substr(0,iInsertLength);
oTR.text = sData;
}
}

function doDragenter(control,length)
{
maxLength = length;
value = control.value;
if(maxLength){
event.returnValue = false;
}
}

function addEvent(elm, evType, fn, useCapture)
{
if (elm.addEventListener)
{
elm.addEventListener(evType, fn, useCapture);
return true;
}
else if (elm.attachEvent)
{
var r = elm.attachEvent('on' + evType, fn);
return r;
}
else {
elm['on' + evType] = fn;
}
}

function AttacheventTextAreaBeforePaste(obj,length)
{
return function()
{
doBeforePaste(obj,length)
}
}

function AttacheventTextAreaPaste(obj,length)
{
return function()
{
doPaste(obj,length)
}
}

function AttacheventTextAreaKeyPress(obj,length)
{
return function()
{
doKeypress(obj,length)
}

}

function AttacheventTextAreaDragEnter(obj,length)
{
return function()
{
doDragenter(obj,length);
}
}

var obj = document.getElementById(controlId);

addEvent(obj,'keypress',AttacheventTextAreaKeyPress(obj,length),null);
addEvent(obj,'beforepaste',AttacheventTextAreaBeforePaste(obj,length),null);
addEvent(obj,'paste',AttacheventTextAreaPaste(obj,length),null);
addEvent(obj,'dragenter',AttacheventTextAreaDragEnter(obj,length),null);
}