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Tolerim
a month ago

After dispatching a successful asynchronous API call, why is the state not updating with the correct data in React-Redux?

As a senior JavaScript developer, I am currently working on a React application that utilizes Redux for state management. I have encountered a problem regarding asynchronous actions. Specifically, I have an action that performs an API call asynchronously and dispatches either a success or error action depending on the outcome. My issue is, even after the success action is dispatched with the correct data, the state is not updating as expected. Here's a sample code that I am using: 
// Action creator
export const fetchData = () => {
  return dispatch => {
    dispatch({ type: 'FETCH_REQUEST' });

    return fetch('https://example.com/data')
      .then(response => response.json())
      .then(data => {
        dispatch({ type: 'FETCH_SUCCESS', payload: data });
      })
      .catch(error => {
        dispatch({ type: 'FETCH_ERROR', payload: error });
      });
  };
};

// Reducer
const initialState = {
  data: null,
  loading: false,
  error: null
};

export const dataReducer = (state = initialState, action) => {
  switch (action.type) {
    case 'FETCH_REQUEST':
      return { ...state, loading: true };
    case 'FETCH_SUCCESS':
      return { ...state, loading: false, data: action.payload };
    case 'FETCH_ERROR':
      return { ...state, loading: false, error: action.payload };
    default:
      return state;
  }
};
To resolve this issue, I would suggest that you double-check if the API endpoint returns the correct data. If yes, you can verify if the dispatched success action is being received by the reducer. You can also check if you are using the correct selector to retrieve the updated state. Additionally, you can inspect the implementation of your component to ensure that everything is working as intended.
Answers(2)
avatar
Vogi
a month ago
Verified Answer
Thank you for sharing your code with me. Based on the code you provided, it seems that the implementation of your asynchronous action creator and reducer is correct. The issue might be related to the way you are using the updated state in your component. Can you provide more details about how you are using the state in your component? Also, can you share the code for your component?
avatar
Tolerim
a month ago
This issue may be caused by mutations to the state object. In the reducer, it is important to always return a new state object with the updated values rather than modifying the existing state object. To ensure that the state updates with the correct data after the success action is dispatched, try using the spread operator to create a new state object rather than modifying the existing state object directly. Modify your reducer code as follows: 
export const dataReducer = (state = initialState, action) => {
  switch (action.type) {
    case 'FETCH_REQUEST':
      return { ...state, loading: true };
    case 'FETCH_SUCCESS':
      // create a new state object with the updated data
      return { ...state, loading: false, data: action.payload };
    case 'FETCH_ERROR':
      // create a new state object with the error message
      return { ...state, loading: false, error: action.payload };
    default:
      return state;
  }
};
This should ensure that the state updates correctly with the data returned from the API.
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