JavaScript to get user typing event for chat programs

<script type="text/javascript" language="javascript">
var timer = 0;
function reduceTimer(){
timer = timer - 1;
isTyping(true);
}
function isTyping(val){
if(val == 'true'){
document.getElementById('typing_on').innerHTML = "User is typing...";
}else{

if(timer <= 0){
document.getElementById('typing_on').innerHTML = "No one is typing -blank space.";
}else{
setTimeout("reduceTimer();",500);
}
}
}
</script>

<label>
<textarea onkeypress="isTyping('true'); timer=5;" onkeyup="isTyping('false')" name="textarea" id="textarea" cols="45" rows="5"></textarea>
</label>
<div id="typing_on">No one is typing -blank speace.</div>