Может
<!DOCTYPE HTML>
<html>
<head> </head>
<body>
<form>
<textarea id="log"></textarea>
</form>
<script>
function log()
{
document.querySelector('#log').value += 'running..\n';
setTimeout(log, 1000);
document.querySelector('#log').blur();
}
log()
</script>
</body>
</html>