ReliableEventsCount.js

fromAll() 
    .when({        
        $init: function () {
            return { count: 0 }; // initial state
        },
        $any: function (state, event) {
            if (event.metadata.EventSourceId.indexOf("$") !== 0) {
                state.count += 1;
            }
            return state;
        } 
    })