useSimpleReducer

useSimpleReducer is the most boilerplate-free way possible to use reducers within a React component.

It’s a simple wrapper on top of useReducer and Redux Toolkit.

Why this is cool:

🌟 It makes the power of reducers as easy to use as useState.
🌟 Use reducers in all your components—it’s so lightweight.

Overview

Here’s a code example

import {useSimpleReducer} from 'use-simple-reducer'

const TextDoubler = () => {

    const initialState = {text: ""}
    const [state, {append, replace}, {doubled}] = useSimpleReducer({
        initialState,
        reducers: {
            append: (newText: string) => (state) => { state.text += newText },
            reset: () => (state) => (initialState)
        }, selectors: {
            doubled: () => (state) => (state.text + state.text)
        }
    })

    return <div>
        <p>Text: {state.text}</p>
        <p>Doubled: {doubled()}</p>
        <button onClick={() => append("hehe")}>Add letters</button>
        <button onClick={() => reset()}>Reset</button>
    </div>
}

All of it is fully type-checked, and uses useReducer and Redux Toolkit under the hood.

Compare this with using:

• useState
• useReducer with Redux Toolkit
• useComplexState

Code snippet comparisons are below.

The point is making it easy & light-weight to use the Commands and Queries design pattern. State is always modified through explicit Command functions, and accessed through Query functions.

Usage

Install the package with:

npm install use-simple-reducer

Then just import it into your code:

import {useSimpleReducer} from "use-simple-reducer"

Now you can use useSimpleReducer in components like this:

import {useSimpleReducer} from 'use-simple-reducer'

const TextDoubler = () => {

    const initialState = {
        text: ""
    }
    const [state, {append, replace}, {doubled}] = useSimpleReducer({

        initialState,
        reducers: {
            append: (newText: string) => (state) => { state.text += newText },
            reset: () => (state) => (initialState)
        }, selectors: {
            doubled: () => (state) => (state.text + state.text)
        }

    })

    return <div>
        <p>Text: {state.text}</p>
        <p>Doubled: {doubled()}</p>
        <button onClick={() => append("hehe")}>Add letters</button>
        <button onClick={() => reset()}>Reset</button>
    </div>
}

Parameters

useSimpleReducer takes a single object with the following fields

• initialState
• reducers
• selectors (optional)

reducers is an object of functions, each of the form

(...args) => (state) => { function_body_here }

function_body_here can either

• return a value to replace state entirely (e.g., return {...state, text: newText))
• or mutate state directly (e.g., state.text += newText).

Internally, useSimpleReducer uses Redux Toolkit and Immer to make sure state isn’t mutated directly, but rather a modified copy is returned. If you’re not sure why that’s useful, read Immer’s documentation.

Similarly, selectors is an object of functions of the form

(...args) => (state) => { function_body_here }

that returns a computed value based on state.

Typing

useSimpleReducer is fully typed. In the above code, Typescript will automatically infer the type of the (state) parameter in your reducers and selectors as {text: string}.

If you want to be explicit about the State type, you can either use a type assertion:

type TodosState = { todos: string[] }

useSimpleReducer({
    initialState: {todos: []} as TodosState,
    ...
})

or extract initialState to an explicitly-typed variable:

type TodosState = { todos: string[] }
const initialState: TodosState = {todos: []}

useSimpleReducer({
    initialState: initialState,
    ...
})

Why this matters

You’ll want to use either of these methods when passing initialState isn’t enough to let Typescript infer the type of your state correctly. For example, if you pass

useSimpleReducer({
    initialState: {todos: []},
    ...
})

Typescript doesn’t know what type todos is an array of, and assumes it to be any[]. This will then throw an error when your reducers or selectors attempt to access todos like an array of strings.

Why can’t you pass in a generics parameter like useSimpleReducer<TodosState>(...)?

You can, but useSimpleReducer uses other generics parameters too, and if you specify one generics parameters, Typescript makes you specify the rest, which gets bulky.

Protip

You can pull out the useSimpleReducer(...) code into your own custom hook, to keep your components even cleaner and better adhere to the Single Responsibility Principle.

import {useSimpleReducer} from 'use-simple-reducer'

const useTextDoubler = () => {

    const initialState = {text: ""}
    const reducers = {
        append: (newText: string) => (state) => { state.text += newText },
        reset: () => (state) => (initialState)
    }
    const selectors = {
        doubled: () => (state) => (state.text + state.text)
    }

    return useSimpleReducer({initialState, reducers, selectors})
}

const TextDoubler = () => {

    const [state, {append, replace}, {doubled}] = useTextDoubler()

    return <div>
        <p>Text: {state.text}</p>
        <p>Doubled: {doubled()}</p>
        <button onClick={() => append("hehe")}>Add letters</button>
        <button onClick={() => reset()}>Reset</button>
    </div>
}

Comparison with alternatives

Consider the following code snippet written with useSimpleReducer

import {useSimpleReducer} from 'use-simple-reducer'

const TodosApp = () => {

    type State = { todos: string[] }
    const initialState: State = {todos: []}

    const [state, {addTodo, setNthTodo}] = useSimpleReducer({
        initialState,
        reducers: {
            addTodo: () => (state) => { state.todos.push(todo) },
            setNthTodo: (index: number, todo: string) => (state) => { state.todos[index] = todo },
        }, selectors: {
            lastTodo: () => (state) => (state.todos.at(-1))
        }
    })

    return <div>
        <ol>
            {state.todos.map((todo, i) => (<li key={i}>
                <input value={todo} onChange={(event) => setNthTodo(i, event.target.value)}/>
            </li>))}
        </ol>
        <button onClick={() => addTodo()}>Add todo</button>
    </div>
}

---

If it was written with useReducer and Redux Toolkit, it would look like:

import {useReducer} from 'react'
import {createSlice} from '@reduxjs/toolkit'

const TodosApp = () => {

    type State = { todos: string[] }
    const initialState: State = {todos: []}

    const slice = createSlice({
        name: "todos",
        initialState,
        reducers: {
            addTodo: (state) => { state.todos.push(todo) },
            setNthTodo: (state, index: number, todo: string) => { state.todos[i] = todo },
        },
    })

    const [state, dispatch] = useReducer(slice.reducer, initialState)

    return <div>
        <ol>
            {state.todos.map((todo, i) => (<li key={i}>
                <input value={todo}
                       onChange={(event) => dispatch(slice.actions.setNthTodo({index: i, todo: event.target.value}))}/>
            </li>))}
        </ol>
        <button onClick={() => dispatch(slice.actions.addTodo())}>Add todo</button>
    </div>
}

Notice the improvements with useSimpleReducer:

1. There’s no need for a name field. Since we are not combining multiple slices together, like you would with redux, this is just unnecessary noise.
2. You pass initialState just once instead of twice, and you can define it inline.
3. No need to wrap the actions with dispatches. That wrapping is ugly, noisy, and easy to mess up (no warning if you call the action without a dispatch—might be a confusing bug to debug).
4. The actions (and selectors, if any) are returned right there in an easy to capture way.
5. When actions take multiple arguments, you can pass them in naturally, like setNthTodo(i, event.target.value), instead of having to wrap them in an object like setNthTodo({index: i, todo: event.target.value}). This is also nice, because if you use IDE refactoring tools, they will rename the parameters correctly in the first case, but might miss the second case.
6. There’s built-in functionality for selectors.

---

If the code snippet was written with useComplexState (a similar library to help reduce boilerplate), it would look like:

import {useComplexState} from 'use-complex-state'

const TodosApp = () => {

    type State = { todos: string[] }
    const initialState: State = {todos: []}

    const [state, {addTodo, setNthTodo}] = useComplexState({
        initialState,
        reducers: {
            addTodo: (state) => { state.todos.push(todo) },
            setNthTodo: (state, index: number, todo: string) => { state.todos[index] = todo },
        },
    })

    return <div>
        <ol>
            {state.todos.map((todo, i) => (<li key={i}>
                <input value={todo} onChange={(event) => setNthTodo({index: i, todo: event.target.value})}/>
            </li>))}
        </ol>
        <button onClick={() => addTodo()}>Add todo</button>
    </div>
}

While points 1–4 are addressed, points 5–6 are not.

---

If the code snippet was written with useState, it might look like:

import {produce} from 'immer'

const TodosApp = () => {

    type State = { todos: string[] }
    const initialState: State = {todos: []}

    const [state, setState] = useState(initialState)
    const addTodo = () => {
        setState(produce(state, (draft) => { state.todos.push(todo) }))
    }
    const setNthTodo = (index: number, todo: string) => {
        setState(produce(state, (draft) => { state.todos[index] = todo }))
    }
    const lastTodo = () => (state.todos.at(-1))

    return <div>
        <ol>
            {state.todos.map((todo, i) => (<li key={i}>
                <input value={todo} onChange={(event) => setNthTodo(i, event.target.value)}/>
            </li>))}
        </ol>
        <button onClick={() => addTodo()}>Add todo</button>
    </div>
}

In React, it’s important not to mutate state directly, but rather to use setState. Thus, you would either have to wrap your action function with produce(...) from Immer, or make sure it doesn’t accidentally mutate the state. This is noisy and easy to get wrong (can lead to difficult to debug behaviours).

In comparison, useSimpleReducer makes it clean and safe to work with state. It also groups together the functionality around a bit of state in a convenient way.