Try
lastEvent = void 0;
heldKeys = {};
window.onkeydown = function(event) {
event = event || window.event; //IE does not pass the event object
if (lastEvent && lastEvent.keyCode === event.keyCode) {
return;
}
lastEvent = event;
heldKeys[event.keyCode] = true;
var keyCode = event.which || event.keyCode; //key property also different
switch (keyCode) {
case 80:
return myamp.userInput("positiv");
case 81:
return myamp.userInput("negativ");
}
};
window.onkeyup = function(event) {
event = event || window.event;
lastEvent = null;
return delete heldKeys[event.keyCode];
};