<!DOCTYPE html>
<html>
<body>

<p>Open "myWindow" and move the new window 250px relative to its current position:</p>

<button onclick="openWin()">Open "myWindow"</button>
<button onclick="moveWin()">Move "myWindow"</button>

<script>
var myWindow;

function openWin() {
    myWindow = window.open("", "myWindow", "width=200, height=100");
    myWindow.document.write("<p>This is 'myWindow'</p>");
}

function moveWin() {
    myWindow.moveBy(250, 250);
    myWindow.focus();
}
</script>

</body>
</html>