<!DOCTYPE html>
<html>
<head>
<script type='text/javascript'>
window.onload=function(){
document.getElementById("b").onclick = function() {
console.log(document.getElementById("t").scrollTop);
};
}
</script>
</head>
<body>
<textarea id="t" rows=10 cols=10> </textarea>
<button id="b">scrollTop</button>
</body>
</html>