javascript textarea MaxLength 属性的实现

// Keep user from entering more than maxLength characters

function doKeyPress(obj, evt) {

    maxLength = obj.getAttribute("maxlength");

    var e = window.event ? event.keyCode: evt.which;

    if ((e == 32) || (e == 13) || (e > 47)) { //IE

        if (maxLength && (obj.value.length > maxLength - 1)) {

            if (window.event) {

                window.event.returnValue = null;

            } else {

                evt.cancelDefault;

                return false;

            }

        }

    }

}

function doKeyUp(obj) {

    maxLength = obj.getAttribute("maxlength");

    if (maxLength && obj.value.length > maxLength) {

        obj.value = obj.value.substr(0, maxLength);

    }

    sr = obj.getAttribute("ShowLength");

    if (sr) {

//        alert((maxLength - obj.value.length));

        document.getElementById(sr).innerHTML = "可填 "+ (maxLength - obj.value.length)+" 字";

    }

}



// Cancel default behavior and create a new paste routine

function doPaste(obj) {

    maxLength = obj.getAttribute("maxlength");

    if (maxLength) {

        var detect = navigator.userAgent.toLowerCase();

        if ((window.event) && (detect.indexOf("safari") + 1 == 0)) { //IE

            var oTR = obj.document.selection.createRange();

            var iInsertLength = maxLength - obj.value.length + oTR.text.length;

            try {

                var sData = window.clipboardData.getData("Text").substr(0, iInsertLength);

                oTR.text = sData;

            } catch(err) {}

            if (window.event) { //IE

                window.event.returnValue = null;

            } else {

                //not IE

                obj.value = obj.value.substr(0, maxLength);

                return false;

            }

        }

    }

}

http://blog.offbeatmammal.com/post/2006/10/26/MaxLength-on-a-Textarea.aspx