In the example below, when the button is pressed, the input field will begin to count (forever), starting at 0.
<html>
<head>
<script type="text/javascript">
var c = 0;
var t;
var timer_is_on = false;
function timedCount() {
document.getElementById('txt').value = c;
c = c + 1;
t = setTimeout(timedCount, 1000);
}
function doTimer() {
if (!timer_is_on) {
timer_is_on = true;
timedCount();
}
}
</script>
</head>
<body>
<form>
<input type="button" value="Start count!" onclick="doTimer()">
<input type="text" id="txt" />
</form>
</body>
</html>
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