index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
</head>
<body>
<button onclick="clickHandler()">打开窗口</button>
<script>
function clickHandler() {
const targetWindow = window.open("./sub.html");
targetWindow.leitang = 1;
alert(targetWindow.opener === window);
}
</script>
</body>
</html>