textbook says: alert (opener.name) can get the name of the parent window.
cat father.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
<script>
window.open("file:///tmp/child.html");
</script>
</body>
i am father window
</html>cat child.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title></title>
<script>
alert(opener.name);
</script>
</head>
<body>
i am child window
</body>
</html>enter file:/tmp/father.html in the browser and child.html will open, but why is there no alert window open?