该onbeforeunload当文档准备好被卸载事件属性”触发。
您可以尝试运行以下代码以实现onbeforeunload属性-
<!DOCTYPE html>
<html>
<body onbeforeunload = "return display()">
<p>Close this window or press F5.</p>
<script>
function display() {
return "Wanna stay here or leave?";
}
</script>
</body>
</html>