const sagaChannelRef = useRef(stdChannel());

runSaga(
  {
    channel: sagaChannelRef.current,
    dispatch: () => {},
    getState: () => {},
  },
  saga
);

const eventsChannel = yield call(getImageLoadingSagas, imgArray);

function getImageLoadingSagas(imagesArray) {
  return eventChannel((emit) => {
    for (const img of imagesArray) {
      const imageChecker = new Image();
      imageChecker.addEventListener("load", () => {
        emit(true);
      });
      imageChecker.addEventListener("error", () => {
        emit(true);
      });
      imageChecker.src = img.url;
    }
    setTimeout(() => {
      //закрытие канала по таймеру
      emit(END);
    }, 100000);
    return () => {
    };
  }, buffers.expanding(10));
}

yield take(eventsChannel);

yield call(putCounter);

function* putCounter() {
  dispatch({
    type: ACTIONS.SET_COUNTER,
    data: stateRef.current.counter + stateRef.current.counterStep,
  });
  yield take((action) => {
    return action.type === "STATE_UPDATED";
  });
}

useEffect(() => {
  ...
    sagaChannelRef.current.put({ type: "STATE_UPDATED" });
  ...
}, [state]);

import { useReducer, useEffect, useRef } from "react";
import { reducer, initialState, ACTIONS } from "./state";
import { runSaga, eventChannel, stdChannel, buffers, END } from "redux-saga";
import { call, take } from "redux-saga/effects";
const PRELOADER_SELECTOR = ".preloader__wrapper";
const PRELOADER_COUNTER_SELECTOR = ".preloader__counter";
const usePreloader = () => {
  const [state, dispatch] = useReducer(reducer, initialState);
  const stateRef = useRef(state);
  const sagaChannelRef = useRef(stdChannel());
  const preloaderEl = document.querySelector(PRELOADER_SELECTOR);
  const counterEl = document.querySelector(PRELOADER_COUNTER_SELECTOR);
  useEffect(() => {
    const imgArray = document.querySelectorAll("img");
    if (imgArray.length > 0) {
      dispatch({
        type: ACTIONS.SET_COUNTER_STEP,
        data: Math.floor(100 / imgArray.length) + 1,
      });
      function* putCounter() {
        dispatch({
          type: ACTIONS.SET_COUNTER,
          data: stateRef.current.counter + stateRef.current.counterStep,
        });
        yield take((action) => {
          return action.type === "STATE_UPDATED";
        });
      }
      function* saga() {
        const eventsChannel = yield call(getImageLoadingSagas, imgArray);
        try {
          while (true) {
            yield take(eventsChannel);
            yield call(putCounter);
          }
        } finally {
          //channel closed
        }
      }
      runSaga(
        {
          channel: sagaChannelRef.current,
          dispatch: () => {},
          getState: () => {},
        },
        saga
      );
    }
  }, []);
  useEffect(() => {
    stateRef.current = state;
    if (stateRef.current.counterStep != 0 && stateRef.current.counter != 0) {
      sagaChannelRef.current.put({ type: "STATE_UPDATED" });
    }
    if (counterEl) {
      stateRef.current.counter < 100
        ? (counterEl.innerHTML = `${stateRef.current.counter}%`)
        : hidePreloader(preloaderEl);
    }
  }, [state]);
  return;
};
function getImageLoadingSagas(imagesArray) {
  return eventChannel((emit) => {
    for (const img of imagesArray) {
      const imageChecker = new Image();
      imageChecker.addEventListener("load", () => {
        emit(true);
      });
      imageChecker.addEventListener("error", () => {
        emit(true);
      });
      imageChecker.src = img.url;
    }
    setTimeout(() => {
      //закрытие канала по таймеру
      emit(END);
    }, 100000);
    return () => {
    };
  }, buffers.expanding(10));
}
const hidePreloader = (preloaderEl) => {
  preloaderEl.remove();
};
export default usePreloader;

import { useReducer, useEffect, useRef } from "react";
import { runSaga, stdChannel, buffers } from "redux-saga";
export function useReducerAndSaga(reducer, state0, saga, sagaOptions) {
  const [state, reactDispatch] = useReducer(reducer, state0);
  const sagaEnv = useRef({ state: state0, pendingActions: [] });
  function dispatch(action) {
    console.log("useReducerAndSaga: react dispatch", action);
    reactDispatch(action);
    console.log("useReducerAndSaga: post react dispatch", action);
    // dispatch to sagas is done in the commit phase
    sagaEnv.current.pendingActions.push(action);
  }
  useEffect(() => {
    console.log("useReducerAndSaga: update saga state");
    // sync with react state, *should* be safe since we're in commit phase
    sagaEnv.current.state = state;
    const pendingActions = sagaEnv.current.pendingActions;
    // flush any pending actions, since we're in commit phase, reducer
    // should've handled all those actions
    if (pendingActions.length > 0) {
      sagaEnv.current.pendingActions = [];
      console.log("useReducerAndSaga: flush saga actions");
      pendingActions.forEach((action) => sagaEnv.current.channel.put(action));
      sagaEnv.current.channel.put({ type: "REACT_STATE_READY", state });
    }
  });
  // This is a one-time effect that starts the root saga
  useEffect(() => {
    sagaEnv.current.channel = stdChannel();
    const task = runSaga(
      {
        ...sagaOptions,
        channel: sagaEnv.current.channel,
        dispatch,
        getState: () => {
          return sagaEnv.current.state;
        }
      },
      saga
    );
    return () => task.cancel();
  }, []);
  return [state, dispatch];
}

import { eventChannel, buffers } from "redux-saga";
import { call, select, take, put } from "redux-saga/effects";
import { ACTIONS, getCounterStep, getCounter, END } from "./state";
export const getImageLoadingSagas = (imagesArray) => {
  return eventChannel((emit) => {
    for (const img of imagesArray) {
      const imageChecker = new Image();
      imageChecker.addEventListener("load", () => {
        emit(true);
      });
      imageChecker.addEventListener("error", () => {
        emit(true);
      });
      imageChecker.src = img.src;
    }
    setTimeout(() => {
      //закрытие канала по таймеру
      emit(END);
    }, 100000);
    return () => {};
  }, buffers.fixed(20));
};
function* putCounter() {
  const currentCounter = yield select(getCounter);
  const counterStep = yield select(getCounterStep);
  yield put({ type: ACTIONS.SET_COUNTER, data: currentCounter + counterStep });
  yield take((action) => {
    return action.type === "REACT_STATE_READY";
  });
}
function* launchLoadingEvents(imgArray) {
  const eventsChannel = yield call(getImageLoadingSagas, imgArray);
  while (true) {
    yield take(eventsChannel);
    yield call(putCounter);
  }
}
export function* saga() {
  while (true) {
    const { data } = yield take(ACTIONS.SET_IMAGES);
    yield call(launchLoadingEvents, data);
  }
}

const SET_COUNTER = "SET_COUNTER";
const SET_COUNTER_STEP = "SET_COUNTER_STEP";
const SET_IMAGES = "SET_IMAGES";
export const initialState = {
  counter: 0,
  counterStep: 0,
  images: [],
};
export const reducer = (state, action) => {
  switch (action.type) {
    case SET_IMAGES:
      return { ...state, images: action.data };
    case SET_COUNTER:
      return { ...state, counter: action.data };
    case SET_COUNTER_STEP:
      return { ...state, counterStep: action.data };
    default:
      throw new Error("This action is not applicable to this component.");
  }
};
export const ACTIONS = {
  SET_COUNTER,
  SET_COUNTER_STEP,
  SET_IMAGES,
};
export const getCounterStep = (state) => state.counterStep;
export const getCounter = (state) => state.counter;

import { useEffect } from "react";
import { reducer, initialState, ACTIONS } from "./state";
import { useReducerAndSaga } from "./useReducerAndSaga";
import { saga } from "./sagas";
const PRELOADER_SELECTOR = ".preloader__wrapper";
const PRELOADER_COUNTER_SELECTOR = ".preloader__counter";
const usePreloader = () => {
  const [state, dispatch] = useReducerAndSaga(reducer, initialState, saga);
  const preloaderEl = document.querySelector(PRELOADER_SELECTOR);
  const counterEl = document.querySelector(PRELOADER_COUNTER_SELECTOR);
  useEffect(() => {
    const imgArray = document.querySelectorAll("img");
    if (imgArray.length > 0) {
      dispatch({
        type: ACTIONS.SET_COUNTER_STEP,
        data: Math.floor(100 / imgArray.length) + 1,
      });
      dispatch({
        type: ACTIONS.SET_IMAGES,
        data: imgArray,
      });
    }
  }, []);
  useEffect(() => {
    if (counterEl) {
      state.counter < 100
        ? (counterEl.innerHTML = `${state.counter}%`)
        : hidePreloader(preloaderEl);
    }
  }, [state.counter]);
  return;
};
const hidePreloader = (preloaderEl) => {
  preloaderEl.remove();
};
export default usePreloader;