<html>
<head>
<script>
var w;
function openwindow()
{
w=window.open('','', 'width=100,height=100');
w.focus();
}
function myFunction()
{
w.resizeTo(500,500);
w.focus();
}
</script>
</head>
<body>
<button onclick="openwindow()">Create window</button>
<button onclick="myFunction()">Resize window</button>
</body>
</html>