HTML 5 - addEventListener Erläuterung

Question

Was bedeutet der folgende Code? Vor allem der "if" Abschnitt. Warum feuert die alert nur manchmal?

window.applicationCache.addEventListener('updateready', function(e) { 
    if (window.applicationCache.status == window.applicationCache.UPDATEREADY) 
    window.location.reload(); 

    alert('done'); 
}, false); 

Jeder Ratschlag ist willkommen.

Answer 1

Siehe Anmerkungen inline:

function foo(e) 
    { 
    /* If the status is UPDATEREADY, reload the page */ 
    if (window.applicationCache.status == window.applicationCache.UPDATEREADY) 
    { 
    window.location.reload(); 
    } 

    /* Alert 'done' (reload has precedence) */ 
    alert('done'); 
    } 

/* Add a new event which bubbles up and calls foo, but does not capture */ 
window.applicationCache.addEventListener('updateready', foo, false); 

Referenzen

• Cordova Issue #5664: AppCache's "checking" event fired more than once per App startup

• Application cache API: UPDATEREADY (numeric value 4)