Listens to an EventEmitter and reduces the data returned.

reduceEventEmmitter.js

/*
Listens to an EventEmitter and reduces the data returned. The EventEmitter must at least three types of events:
- dataEvent: it sends the data to be reduced
- endEvent: it signals the completion of the operation
- errorEvent: it sends an error. The operation is interrupted to handle it
*/
function reduceEventEmmitter({dataEvent, endEvent, errorEvent = null}, accumulator = [], reducer, eventEmitter, cb) {
    eventEmitter.on(dataEvent, function handleDataEvent(data) {
        accumulator = reducer(accumulator, data);
    });

    eventEmitter.on(endEvent, function handleEndEvent() {
        cb(null, accumulator);
    });

    if (errorEvent) {
        eventEmitter.on(errorEvent, function handleEndEvent(error) {
            cb(error);
        });
    }
}