Замыкание тебе в помощь
<!DOCTYPE html>
<html lang="ru">
<head>
<meta charset="UTF-8"/>
<title>Glob</title>
<script type="text/javascript">
window.onload = function() {
var ClickCounter = 0;
document.addEventListener("click", function(e) {
ClickCounter++;
document.getElementById('my').innerHTML = ClickCounter;
});
};
</script>
</head>
<body>
<div id="my"></div>
</body>
</html>