如何區分onUnload事件中頁面刷新和瀏覽器關閉？

<code class="javascript">function myLoad(event) {
    if (window.localStorage) {
        var t0 = Number(window.localStorage['myUnloadEventFlag']);
        if (isNaN(t0)) t0=0;
        var t1=new Date().getTime();
        var duration=t1-t0;
        if (duration<10*1000) {
            // It's a browser reload
        } else {
            // It's a browser close
        }
    }
}</code>

<code class="javascript">function myUnload(event) {
    if (window.localStorage) {
        // Flag the page as unloading
        window.localStorage['myUnloadEventFlag']=new Date().getTime();
    }

    // Notify the server to disconnect the user in a few seconds
    askServerToDisconnectUserInAFewSeconds();
}</code>