Checking existing state in a Redux Saga

saga.js

import { takeEvery } from 'redux-saga';
import { put, select } from 'redux-saga/effects';

/*
 * Select data from state. The return object depends on your state shape
 */
export const getLessons = state => state.lessons;

/*
 * Our worker Saga: will perform the async lessons/EDIT task
 */
export function* editLessonAsync(action) {
  const { id, title } = action.lesson;
  const lessons = yield select(getLessons);

  /*
   * Arbitrarily dispatch a lessons/NEW event if the lesson we're editing exists in state.
   */
  if ( Object.keys(lessons).includes(id) ) {
    yield put( 'lessons/NEW' );
  }
}

/*
 * Our watcher Saga: spawn a new editLessonAsync task on each lessons/EDIT
 */
export function* watchEditLesson() {
  yield takeEvery('lessons/EDIT', editLessonAsync);
}

/*
 * Single entry point to start all Sagas at once
 */
export default function* rootSaga() {
  yield [
    watchEditLesson(),
  ];
}