React State Management Cheat Sheet

The quest for the ideal React state management is one of the most discussed topics in the React community. If you look around, you will often come across the following question: How do I manage my state in React?^[1]n00b Q: Why would you ever use React w/o Hooks?

Contents

1 What is State Management?

2 What does state mean in React?

3 Is there an official / recommended state management solution like other frameworks in React?

4 So how does one choose the appropriate state management solution?

5 useState

6 useReducer

7 Context API + State hooks

8 Server-State (react-query, Apollo, swr).

9 Redux et al.

10 Conclusion

Especially devs who previously worked with other frameworks like Angular or Vue ask themselves how to manage their state in React. Often the question comes about an official solution for state management.^[2]State management in React?

Another question devs have been asking since the introduction of the Context API and Hooks API in React 16.8 is deciding between Redux or the Context API with useState/useReducer to manage its global state.^[3]Is redux really a good idea?

I would like to answer both questions in the following. For this purpose, I did some research in the community and got the opinion of many experienced React developers.

What is State Management?

Before we begin, however, I would like to clarify a few basic points. Before we can solve the question of the right state management, I think we need a definition of what exactly state management means.

The state describes the condition of an application at a given point in time.

Sub-types of the state are:

Server State,
navigation state
local UI state
global UI state

Accordingly, state management describes the maintenance of the state/knowledge of an application depending on all inputs.^[4]Virdol, Martin – How To Simplify Your Application State Management

Inputs usually take place on the server (API) or the client (user).

Accordingly, the difficulty of state management arises from the coordination of all subtypes of state in an application.^[5]Virdol, Martin – How To Simplify Your Application State Management

What does state mean in React?

The UI is the visual representation of the state of an application. As described above, State represents the state of an application at a given point in time.^[6]Wieruch, Robin -React State Management

It follows that: In React the State is a data structure that reflects the current state of the UI.

The State can consist of different kinds of data:

A Boolean that decides whether a sidebar is open or not.
The text content of a form.
Server data pulled via an API.

In JavaScript, we can represent this as follows:

// 1)
let isOpen = false;

// 2)
let addressForm = {
  first: "Donald", 
  last: "Duck",
  street: "Webfoot Walk",
  no: "1313",
  town: "Duckburg",
  state: "Calisto",
};

// 3)
const issues = [
  {
    "url": "https://api.github.com/repos/rockiger/metado/issues/47",
    "number": 47,
    "title": "Look into warnings from react beautiful dnd",
    "body": "",
    ...
  },
  ...
  {
    "url": "https://api.github.com/repos/rockiger/metado/issues/46",
    "number": 46,
    "title": "Create Testsystem for metado",
    "body": "- [ ] https://firebase.google.com/docs/emulator-suite\n",
    ...
  },
]

All this data could be managed either locally (i.e. within a component using React hooks or setState) or globally.

In this case, managing means saving and changing the state, as well as displaying the state through the UI.

Is there an official / recommended state management solution like other frameworks in React?

Yes and no. With the setState method and the useState/useReducer hooks, there is a React-specific solution for local state management within a component. With this, you can already create reasonably complex apps^[7]Should I use a state management library like Redux or MobX?.

There is no quasi-official solution for global state management like NgRx for Angular or Vuex for Vue. Here, you are spoiled for choice with React. Some solutions are specialized for certain parts of the application state (e.g. react-query), some are general solutions (e.g. Redux).^[8]Erikon, Mark – When (and when not) to reach for Redux

So how does one choose the appropriate state management solution?

I would like to deliberately leave Navigation-State out of this consideration. Any React application that has more than two views should rely on a routing library like react-router. From my point of view, handling the browser API is way too complex to manage it by yourself.

If we assume that the main difficulty is coordinating the subtypes, then the first thing we should ask ourselves is: what types of state do we need to manage in our (React) application? How complex is my state? How often does it change? And then we decide which solution is best for us.

Below you can see a diagram of my decision process.

Decision process for choosing the right state management solution.

useState

The first question we ask is: Is our State shared by more than two components? If we answer in the negative, the question is: does our state have complex update logic, i.e. is the new state dependent on the old state or are multiple subvalues changed? If we also deny this, we use local state with useState.

For example, if we have a simple counter with one component, the use of local state with useState is sufficient.

function Counter({initialCount: 42}) {
  const [count, setCount] = useState(initialCount);
  return (
    <>
      Count: {count}
      <button onClick={() => setCount(initialCount)}>Reset</button>
      <button onClick={() => setCount(prevCount => prevCount - 1)}>-</button>
      <button onClick={() => setCount(prevCount => prevCount + 1)}>+</button>
    </>
  );
}

When the Counter component is rendered for the first time, the useState hook is initialized with intialCount. As return value we get the state variable count and the update function setCount.

To change count, we need to call setCount with a new value. Whenever we call setCount, the counter component is re-rendered.

If we want to set the new value of count based on the old one, we should pass setCount a simple update function that passes the new value of count as its return value.

Exercises

Read about useState in the React docs.
Work through the useState guide

useReducer

Now, unlike our example above, if our state has complex update logic, it makes sense to useReducer.

As described above, complex in this context means that a change of the state must change many values of the state or that the state depends on the previous state.

const initialState = {count: 0};

function reducer(state, action) {
  switch (action.type) {
    case 'increment':
      return {count: state.count + 1};
    case 'decrement':
      return {count: state.count - 1};
    case 'set':
      return {count: action.count};
    case 'reset':
      return initialState;
    default:
      state;
  }
}

function Counter() {
  const [state, dispatch] = useReducer(reducer, initialState);
  return (
    <>
      Count: {state.count}
      <button onClick={() => dispatch({type: 'reset'})}>Reset</button>
      <button onClick={() => dispatch({type: 'decrement'})}>-</button>
      <button onClick={() => dispatch({type: 'increment'})}>+</button>
      <button onClick={() => dispatch({type: 'set', count: 25})}>Set to 25</button>
    </>
  );
}

First we define an initial state and a pure reducer function. This consumes a state and an action and returns a new state.

To use useReducer in our counter component, we proceed similarly as with useState: We initialize useReducer with initalState and reducer. After the initialization we get back the state and a dispatch function. The dispatch function is used to request a state change from the reducer. For this we call dispatch with an appropriate action.

Accordingly, the onClick handlers of the buttons no longer contain their own logic, but only request the state change via dispatch.

Exercises

Context API + State hooks

If we look at the right part of the decision diagram, that is, if we answered yes to the question “Is the state shared by more than two components?”, we are faced with the question of whether our global state changes frequently? If we can answer this in the negative, the Context API can make our lives easier.

A typical example is the login state of a user. Which is needed in many different components.

// Auth.js
const AuthContext = createContext({username: '', role: ''});

export function useAuth() {
  const context = useContext(AuthContext);
  if (!context) {
    throw new Error('useAuth must be used within a AuthProvider');
  }
  return context;
}

export function AuthProvider({ children }) {
  const [user, setUser] = useState({username: '', role: ''});

  return (
    <AuthContext.Provider value={{ user }}>
      {children}
    </AuthContext.Provider>
  );
}

// App.js
export function App() {
  return (
    <AuthProvider>
      <Component />
    </AuthProvider>
  );
}

// Component.js
export function Component() {
  const { user } = useAuth()
  if (user?.role === 'ADMIN') {
    return <AdminView />
  } else {
    return <UserView />
  }
}

In our code example, we initialize the context with createContext, which we make available to all children of the AuthProvider component.

With the custom hook useAuth, the child components can access the state. This allows us to save unnecessary prop drilling.

Tasks

Read more about React’s useContext hook in the React docs.
Read more about useContext combined with useState and useReducer

Server-State (react-query, Apollo, swr).

Looking at our decision diagram again, we see that we have used up React’s board resources. We are now moving into the area where it may be worthwhile to use external state management solutions.

If an application uses global state primarily to retrieve, cache, and update data residing on a server, it is recommended to use a specialized data management solution.^[9]Dodds, Kent – Application State Managment with React

In an admin interface, we often need to display many different data in different views. Managing this data efficiently can be anything but trivial.^[10]Overview react-query

In the following, I would like to show a simple example using react-query.

// App.js
import { QueryClient, QueryClientProvider} from 'react-query'

const queryClient = new QueryClient()

export default function App() {
  return (
    <QueryClientProvider client={queryClient}>
      <Component />
    </QueryClientProvider>
  )
}

// Component.js
import { useQuery } from 'react-query'

function Component() {
  const { isLoading, error, data } = useQuery('issues', () =>
    fetch('https://api.github.com/repos/rockiger/metado').then(res =>
      res.json()
    )
  )

  if (isLoading) return 'Loading...'

  if (error) return 'An error has occurred: ' + error.message

  return (
    <>
      <h1>{data.name}</h1>
      <p>{data.description}</p>
    </>
  );
}

Similar to our context API example, react-query provides us with a context provider and a custom hook.

With the custom hook useQuery we can now fetch the data we need. For this we pass useQuery a unique name and the actual fetch function. We get back the data (status, error, content) we need to display.

The real highlight is that react-query takes over the management for us. It makes sure that the data is cached and updated automatically. If we use the same query issues in a second component, react-query will not execute the query multiple times, but will fall back on the cached data.^[11]Important Defaults – react-query

In addition, the provided context provider is optimized to prevent unnecessary re-rendering of components. Implementing this functionality yourself is far from straightforward.^[12]On Cache Invalidation – Why is it hard?

Tasks

Learn more about the motivation behind react-query
Learn about the alternatives Apollo and SWR

Redux et al.

But what do you do if the state is shared by multiple components, changes frequently, and is not mainly server state?

For example, to manage the state in a text editor with many buttons. This is where Redux comes in. Redux is very efficient, has a large ecosystem with many plugins (so-called middleware) and is very well documented.

import React from 'react'
import { useDispatch, useSelector } from 'react-redux'
import { createSlice } from '@reduxjs/toolkit'

// 1) Create state and actions/reducers
const counterSlice = createSlice({
  name: 'counter',
  initialState: {
    value: 0,
  },
  reducers: {
    incremented: (state) => {
      return {value: state.value + 1};
    },
    decremented: (state) => {
      return { value: state.value - 1 };
    },
  },
})

export const { incremented, decremented } = counterSlice.actions

// 2) select and dispatch
export const Count = () => {
  const count = useSelector(state => state.counter.count)
  const dispatch = useDispatch()

  return (
    <main>
      <div>Count: {count}</div>
      <button onClick={() => dispatch(incremented())}>Decrement</button>
      <button onClick={() => dispatch(decremented())}>Increment</button>
    </main>
  )
}

We reimplement our counter example here again using Redux and the Redux toolkit. It is very similar to the useReducer variant.

First, we initialize our state and our reducer. In our Counter component, we initialize a so-called selector; a function to select a subset of the state. Additionally, we use the useDispatch hook of Redux to be able to command state changes.

Unlike our useReducer variant, we do not need to name an action with a string. Action names are automatically generated by createSlice.

As our simple counter example shows, setting up Redux does require a bit more effort. So that since the official introduction of the Context API in React 16.3, it is mostly not worth the effort for small application.

The advantages of Redux over the combination of Context API and React hooks are:^[13]Erikson Marc – Blogged Answers: Redux – Not Dead Yet!

consistent and defined architectural patterns that can facilitate teamwork
easy debugging through the excellent browser extension
the use of different middleware
many add-ons and good extensibility
the cross-platform and cross-framework usage
depending on the app state, better performance than the Context API

While Redux is the best known and most popular state management solution for React, it is by no means the only one. Alternatives include: MobX, Recoil, RxJS.

Tasks

Learn more about using von Redux und Redux-Toolkit.
Research Redux alternatives

Conclusion

It doesn’t always have to be Redux. Many React applications can get by without Redux. In many cases, using Redux adds unnecessary complexity.

React hooks and the Context API can cover many use cases that were previously solved with Redux

A specialized library is recommended for server-state caching.

The decision diagram can help developers find the right form of state management for their application.

Finally, the solutions shown are not mutually exclusive. There is nothing wrong with using local and global state in your application.

References[+]

References
↑1	n00b Q: Why would you ever use React w/o Hooks?
↑2	State management in React?
↑3	Is redux really a good idea?
↑4, ↑5	Virdol, Martin – How To Simplify Your Application State Management
↑6	Wieruch, Robin -React State Management
↑7	Should I use a state management library like Redux or MobX?
↑8	Erikon, Mark – When (and when not) to reach for Redux
↑9	Dodds, Kent – Application State Managment with React
↑10	Overview react-query
↑11	Important Defaults – react-query
↑12	On Cache Invalidation – Why is it hard?
↑13	Erikson Marc – Blogged Answers: Redux – Not Dead Yet!

What is State Management?

What does state mean in React?

Is there an official / recommended state management solution like other frameworks in React?

So how does one choose the appropriate state management solution?

useState

Exercises

useReducer

Exercises

Context API + State hooks

Tasks

Server-State (react-query, Apollo, swr).

Tasks

Redux et al.

Tasks

Conclusion

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