foo.js

export const searchWatchStart = (searchConstants, selectSearch, apiFn, handleError) => {
  const searchCreators = createRequestCreators(searchConstants.FETCH_STATUS);
  const loadResults = fetchEntity.bind(null, searchCreators, apiFn, { handleError });
  const selectMask = makeSelectMask(selectSearch);

  return function* () { // eslint-disable-line func-names
    let lastTask;
    for (;;) {
      const { wait } = yield take(searchConstants.START_SEARCH);

      if (lastTask) {
        yield cancel(lastTask);
      }

      const searchMask = yield select(selectMask);

      lastTask = yield fork(function* () { // eslint-disable-line func-names
        if (wait) {
          yield call(delay, wait);
        }

        yield call(loadResults, searchMask);
      });
    }
  };
};