关闭浏览器或后退时页面提醒

1. <script>
   
2.   (()=>{
   
3.     window.onbeforeunload = (event) => {
   
4.       return "关闭前的提示";
   
5.       // delete event['returnValue']
   
6.     }
   
7.   })()
   
8. </script>

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