Onbeforeunload也是在頁面重新整理或關閉時調用，Onbeforeunload是正要去伺服器讀取新的頁面時調用，此時還沒開始讀取；而 onunload則已經從伺服器上讀到了需要載入的新的頁面，在即將替換掉當前頁面時調用。Onunload是無法阻止頁面的更新和關閉的。而 Onbeforeunload 可以做到。曾經做一個考試系統，涉及到防止使用者半途退出考試（有意或者無意），代碼如下：
window.onbeforeunload = onbeforeunload_handler;<br /> window.onunload = onunload_handler;<br /> function onbeforeunload_handler(){<br /> var warning="確認退出?";<br /> return warning;<br /> } </p><p> function onunload_handler(){<br /> var warning="謝謝光臨";<br /> alert(warning);<br /> } 這段代碼在FF和IE上都能正確執行.再點擊關閉按鈕時首先觸發obbeforeunload事件,點擊否定時不執行onload事件. 通常應用在 登出session等等登陸資訊 等方面....這裡一併推薦一個ActionScript3的好教程:http://gskinner.com/talks/as3workshop 寫道運用onunload事件判斷瀏覽器是重新整理還是關閉視窗function CloseOpen(event) {<br /> if(event.clientX<=0 && event.clientY<0) {<br /> alert("關閉");<br /> }<br /> else<br /> {<br /> alert("重新整理或離開");<br /> }<br />}另外一種判斷重新整理和關閉的方法window.onbeforeunload = function() //author: meizz<br />{<br /> var n = window.event.screenX - window.screenLeft;<br /> var b = n > document.documentElement.scrollWidth-20;<br /> if(b && window.event.clientY < 0 || window.event.altKey)<br /> {<br /> alert("是關閉而非重新整理");<br /> window.event.returnValue = ""; //這裡可以放置你想做的作業碼<br /> }else<br /> {<br /> alert("是重新整理而非關閉");<br /> }<br />} 博文來源：http://www.javaeye.com/topic/269213Start building with 50+ products and up to 12 months usage for Elastic Compute Service
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