Convert useState to useReducer in a React Context

Posted by Peter G Kellner on April 19, 2022 · 1 min read

Often, we find ourselves in a situation where we’ve coded with useState and we want more capability integrated into our change. That is, we may want to add a logging statement that outputs the original value and the changed value, or even store that change someplace as history. useReducer is perfect for this, but as it’s parameters feel quite different. Luckily, since useState is actually built with useReducer, it is very possible to make this conversion.

The Original Code That Uses useState

export const DisplayCountContext = createContext();

function DisplayCountProvider({ children, initialDisplayCount }) {
  const [displayCount, setDisplayCount] = useState(initialDisplayCount);
 
  const contextValue = {
    displayCount,
    setDisplayCount,
  };
  
  return (
    <DisplayCountContext.Provider value={contextValue}>
      {children}
    </DisplayCountContext.Provider>
  );
}

export { DisplayCountProvider };

The Equivalent Code Using useReducer

export const DisplayCountContext = createContext();

function DisplayCountProvider({ children, initialDisplayCount }) {
  
  function reducer(state, action) {
    let newState;
    switch (action.type) {
      case "setDisplayCount":
        newState = { ...state, displayCount: action.payload };
        break;
      default:
        throw new Error();
    }
    return newState;
  }
  
  const [state, dispatch] = useReducer(reducer, {
    displayCount: initialDisplayCount,
  });

  const setDisplayCount = (val) => {
    // put your extra logging type code
    // like: console.log(`Original Value:${displayCount}  New Value: ${val}`)
    dispatch({ type: "setDisplayCount", payload: val });
  };

  const contextValue = {
    displayCount: state.displayCount,
    setDisplayCount,
  };

  return (
    <DisplayCountContext.Provider value={contextValue}>
      {children}
    </DisplayCountContext.Provider>
  );
}

export { DisplayCountProvider };

That’s literally it.