<!DOCTYPE html>
<html>
<body>

<button onclick="openWin()">Open "myWindow"</button>
<button onclick="closeWin()">Close "myWindow"</button>

<script>
var myWindow;

function openWin() {
    myWindow = window.open("", "myWindow", "width=200, height=100");
}

function closeWin() {
    myWindow.close();
    myWindow.close();
}
</script>

</body>
</html>