js按键频率解决event兼容性问题

JScript code

function KeyCombination() {    this.Length = 0;    this.Records = new Array();}KeyCombination.prototype.Count = function() {    return this.Length;}KeyCombination.prototype.AddKeyRecord = function(recordKey) {    if (!this.Contains(recordKey)) {        this.Records.push(new KeyRecord(recordKey));    }};KeyCombination.prototype.GetKeyRecord = function(recordKey) {    return this.Records[this.IndexOf(recordKey)];};KeyCombination.prototype.Contains = function(recordKey) {    return this.IndexOf(recordKey) > -1;};KeyCombination.prototype.IndexOf = function(recordKey) {    var ind = -1;    var r;    for (var i=0, len=this.Records.length; i<len; i++) {        r = this.Records[i];        if (r.Name === recordKey) {            ind = i;            break;        }    }    return ind};KeyCombination.prototype.WriteKeyRecord = function(keyCode, timeStamp) {    if (this.IsFull())        this.ClearAllRecords();    var r;    for (var i=0, len=this.Records.length; i<len; i++) {        r = this.Records[i];        if (r.IsEmpty()) {            r.SetValue(keyCode, timeStamp);            this.Length++;            break;        }    }};KeyCombination.prototype.IsFull = function() {    return this.Length == this.Records.length;};KeyCombination.prototype.ClearAllRecords = function() {    var r;    for (var i=0, len=this.Records.length; i<len; i++) {        r = this.Records[i];        r.Clear();    }    this.Length = 0;};function KeyRecord(name) {    this.Name = name;    this.KeyCode = null;    this.TimeStamp = null;}KeyRecord.prototype.IsEmpty = function() {    return this.KeyCode === null;};KeyRecord.prototype.SetValue = function(keyCode, timeStamp) {    this.KeyCode = keyCode;    this.TimeStamp = timeStamp;};KeyRecord.prototype.Clear = function() {    this.KeyCode = null;    this.TimeStamp = null;};var MAX_INTERVAL = 3000;var keyComb = new KeyCombination();keyComb.AddKeyRecord("first");keyComb.AddKeyRecord("second");document.documentElement.onkeyup = function() {    keyComb.WriteKeyRecord(event.keyCode, new Date());    if (keyComb.IsFull()) {        var interval = keyComb.GetKeyRecord("second").TimeStamp - keyComb.GetKeyRecord("first").TimeStamp;            var info = interval;            alert(interval);    var request =getHttpObject();    request.open("get","http://localhost/guosai/final/final.php?keyboard="+info,true);    request.setRequestHeader('Content-Type', 'text/xml;charset=UTF-8');    request.send(info);    }};

发现event代码在FF下存在兼容性问题，求解决~

[解决办法]
document.documentElement.onkeyup = function(evt) {
var event = evt || event;
keyComb.WriteKeyRecord(event.keyCode, new Date());