React-Redux - No reducer provided for key “coins”

Question

Not sure why I'm getting the following errors.

I'm just setting up my store, actions and reducers, I haven't called dispatch on anything yet.

Expected

App runs fine, Redux state is not updated

Results

src/index.js

import React from 'react'
import ReactDOM from 'react-dom'

import { createStore, applyMiddleware, compose } from 'redux'
import { Provider } from 'react-redux'
import thunk from 'redux-thunk'
import reducer from './reducer'

import App from './App'
import css from './coinhover.scss'

const element = document.getElementById('coinhover');

const store = createStore(reducer, compose(
    applyMiddleware(thunk),
    window.__REDUX_DEVTOOLS_EXTENSION__ && window.__REDUX_DEVTOOLS_EXTENSION__()
));

ReactDOM.render(
    <Provider store={ store }>
        <App />
    </Provider>, element);

src/reducer/index.js

import { combineReducers } from 'redux'
import { coins } from './coins'

export default combineReducers({
    coins
});

src/reducer/actions/coins.js

import * as api from '../../services/api'
import { storage, addToPortfolio } from '../../services/coinFactory'

export const ADD_COIN = 'ADD_COIN'

export function getCoin(coin) {
    return dispatch => {
        api.getCoin(coin)
            .then((res_coin)  => addToPortfolio(res_coin))
            .then((portfolio) => dispatch(updatePortfolio(portfolio)));
    }
}

export function updatePortfolio(portfolio) {
    return {
        type: ADD_COIN,
        portfolio
    }
}

finally src/reducer/coins/index.js

import { ADD_COIN } from './actions'

const initialState = [];

export default (state = initialState, action) => {
    switch(action.type) {
        case ADD_COIN:
            return action.portfolio;
        default:
            return state;
    }
}

Answer 1

Your issue lies with how you're importing your coins reducer:

import { coins } from './coins'

The latter tries to obtain a named export returned from the file in ./coins.

You are not using any named exports only export default, therefore you just need to import the file as follows:

import coins from './coins';

Using the latter will result with the fact that coins will then contain the value of export default; which will be the coins reducer.

Answer 2

Even when all your imports are correctly imported, this can still happen for one other reason. Circular Dependency!

In my case, this happeded because of a circular dependency in a file. I had two circular dependecy in the project that I created accedentally. Example: rootReducer.ts -> authSlice.ts -> rootReducer.ts.

These dependencies are often not as easy to debug. I used this package to check for circular dependencies. Once the circular dependency was removed, all was well.

Answer 3

Ah just found it, I was importing my coins reducer incorrectly...

import { combineReducers } from 'redux'
import coins from './coins' // because I have coins/index.js

export default combineReducers({
    coins
});

instead of

import { coins } from './coins'

Answer 4

This was my fix:

import { combineReducers } from 'redux'
import { coins } from './coins'

export default combineReducers({
    coinsState: coins || (() => null) // By adding this I resolved it.
});

Answer 5

In my case, I was not adding a default property to my reducers. When I added it, it worked. here is my code;

const counterReducer = (state = 0, action) => {
    switch(action.type){
      case 'INCREMENT':
        return state + 1;
      case 'DECREMENT':
          return state - 1;
      default:
        return state;    
    }
  }
  
export default counterReducer;

and combinde file;

import   counter   from './counter';
import { combineReducers } from 'redux';

const allReducers = combineReducers({
    counter: counter,
   
});

export default allReducers;