React.useState() vs React.useReducer()

Written byPhuoc Nguyen

#React.useState()

If you're working with React, `useState` is the easiest way to manage state. It's a hook that gives you two things: the current state and a function to update it. You can set the initial state to `null`, `undefined`, or an empty string, or pass in a value of your own.

Let's say you're building a table with search, filter, and pagination features. You'll need some variables to keep track of the data, search queries, filters, and page numbers.

To manage all of these, you can use multiple `useState` hooks. For example, you might use `data`, `query`, `filter`, and `page` properties to keep track of each piece of state. You can use the `fetchData` function to call an API and get the data based on the search query and filter.

As users interact with the table, you'll need to update the state values based on the input. You can use functions like `handleSearch`, `handleFilter`, and `handlePageChange` to update the state. Sometimes you'll need to update multiple states at once – for example, when users search for something or apply filters, you'll need to reset the page index to 1.

Finally, the table will be rendered with data based on the current page and page size properties of the state using pagination functionality.

Here's an example of how you can use multiple `useState` hooks to manage state in this scenario:

import * as React from 'react';

export const Table = () => {
    const [data, setData] = React.useState([]);
    const [query, setQuery] = React.useState('');
    const [filter, setFilter] = React.useState({});
    const [page, setPage] = React.useState(1);

    const fetchData = () => {
        // Make API call with query and filter
        // update data with response
    };

    const handleSearch = (event) => {
        setQuery(event.target.value);
        setPage(1);
    };

    const handleFilter = (filterObj) => {
        setFilter(filterObj);
        setPage(1);
    };

    const handlePageChange = (pageNum) => {
        setPage(pageNum);
    };

    useEffect(() => {
        fetchData();
    }, [query, filter]);

    // Render table with data based
    // on current page and page size
    return (...);
};

As you can see, the implementation can get more complex as more features are added.

#React.useReducer()

The `useReducer` hook is a powerful tool that helps manage complex state and actions in a predictable way. It follows the reducer pattern used in Redux, which is a well-known state management library.

To use `useReducer`, you just need to provide it with two arguments: a reducer function and an initial state. The `reducer` function handles updates to the state, while `state` holds the current state. With the `useReducer` method, we only need one variable to manage all internal states.

To send actions to the reducer, we use the `dispatch` function. The action object passed to `dispatch` includes a `type` property that specifies which action to perform, and a `payload` property that can be used to pass any additional data needed by the reducer function.

When an action is dispatched, React calls the reducer function with the current state and the action object as arguments. The reducer function then returns a new state based on both pieces of information.

Let's take a look at how we can use `useReducer` to manage state in a more predictable way. We'll be using this hook to rewrite the previous example.

import * as React from 'react';

const reducer = (state, action) => {
    switch (action.type) {
        case 'SET_DATA':
            return { ...state, data: action.payload };
        case 'SET_QUERY':
            return { ...state, query: action.payload };
        case 'SET_FILTER':
            return { ...state, filter: action.payload };
        case 'SET_PAGE':
            return { ...state, page: action.payload };
        default:
            throw new Error();
    }
};

const Table = () => {
    const [state, dispatch] = React.useReducer(reducer, {
        data: [],
        query: '',
        filter: {},
        page: 1,
        pageSize: 10
    });

    const fetchData = () => {
        // Make API call with state.query and state.filter
        // update state.data with response
    };

    const handleSearch = (event) => {
        dispatch({
            type: 'SET_QUERY',
            payload: event.target.value,
        });
    };

    const handleFilter = (filterObj) => {
        dispatch({
            type: 'SET_FILTER',
            payload: filterObj,
        });
    };

    const handlePageChange = (pageNum) => {
        dispatch({
            type: 'SET_PAGE',
            payload: pageNum,
        });
    };

    useEffect(() => {
        fetchData();
    }, [state.query, state.filter]);

    // Render table with state.data based
    // on current page and page size
    return (...);
};

In this example, when a user searches for something or applies filters to the results, we use `dispatch` to update multiple states at once. If a user types something in the search input field and presses enter, we call the `handleSearch` method with the event value as the payload parameter.

const handleSearch = (event) => {
    dispatch({
        type: 'SET_QUERY',
        payload: event.target.value,
    });
};

The `dispatch` method sends an object with type `SET_QUERY` and payload equal to the event's target value. This will trigger our reducer method and update our query state.

The reducer takes two parameters: the current state and an action object that has `type` and `payload` properties. In the example above, it checks if the type of the incoming action matches the string `SET_QUERY`. If it does, it updates the query property of our state with the payload parameter's value.

const reducer = (state, action) => {
    switch (action.type) {
        case 'SET_QUERY':
            return { ...state, query: action.payload };
        default:
            throw new Error();
    }
};

Using this state management technique can make your code more predictable since all changes are made through actions that are handled by a single function. This approach also simplifies debugging by allowing you to easily track which actions were performed on your state at any given time during your application's lifecycle.

#Conclusion

To sum up, both `useState` and `useReducer` hooks are useful for managing state in React. Which one you choose depends on your state management needs.

For simple state changes that don't require much logic or coordination, `useState` is the way to go. But if you're dealing with complex state changes that require coordination between different parts of your app, `useReducer` is your best bet.

Neither hook is better than the other; they simply have different strengths. By understanding these differences, you can decide which one to use in your own projects.

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