javascript textarea MaxLength 属性的实现

代码

// 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