// userSignups is array of event_ids user is subscribed to
// events is app's array of events
var uLen = userSignups.length;
var eLen = events.length;
for (var u = 0; u < uLen; u++) {
    var subscribedID = userSignups[u].event_id;
    if (!subscribedID) { continue; }
    for (var e = 0; e < eLen; e++) {
        if (events[e].event_id === subscribedID) {
            events[e].subscribed = true;
            break;
        }
    }
}