為了防止使用者不小心關閉瀏覽器視窗，或者我們想在瀏覽器視窗關閉的時候做一些事，那麼我們會使用到window物件的onbeforeunload和onunload。

<script type="text/javascript">  

	showValue();
	
    window.onbeforeunload = onbeforeunload_handler;  
    window.onunload = onunload_handler;  
		
    function onbeforeunload_handler(){  
		return "Are sure to leave?"
    }  
      
    function onunload_handler(){  
        storeValue("hehehe"); 
    }  
	
	function showValue()
	{
		var localStorage = window.localStorage;  	
		alert(localStorage.getItem("key"));
	}
	
	function storeValue(value)
	{
		var localStorage = window.localStorage;  
        localStorage.setItem("key",value);  
	}
 
</script>