Which event to catch for application shut down?

I am using jQueryMobile and phoneGap for a cross-device mobile application. I use html 5 local storage to persist records that worked on by user.

I don't know which phoneGap event to catch just before application shut-down so I can make sure data is saved before shutdown completes.

Base on suggestion from naughtur, I tried both unload and beforeunload events, neither of them got fired during app shutdown. Following is my code snip:

function persistTasks(){
    alert ("is unloading the app");
    offlineTasklist.set("tasks", tasklist); 
}

function init() {
    document.addEventListener("unload", persistTasks, false);
    login();
}

$(document).ready(init);