trackqueries.ts

function trackQueryEvents(queries: Observable<Query[]>): Observable<QueryEvent> {
  var oldQueries = [];
  return queries.flatMap((queries: Query[]) => {
    var res = Observable.fromArray([]
    .concat(queries
      .filter(query =>
        oldQueries.find(oldQuery => oldQuery.match(query)) === undefined)
      .map(query => {event: 'added', query}))
    .concat(oldQueries
      .filter(oldQuery => queries.find(query => query.match(oldQuery)) === undefined)
      .map(oldQuery => {event: 'removed', query})));
    oldQueries = queries;
    return res;
  });
}