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);
}