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---title: Reducernav: 3.99keywords: reducer,action,dispatchpublished: false---
## atomWithReducer
Ref: https://github.com/pmndrs/jotai/issues/38
```jsimport { atomWithReducer } from 'jotai/utils'
const countReducer = (prev, action) => {  if (action.type === 'inc') return prev + 1  if (action.type === 'dec') return prev - 1  throw new Error('unknown action type')}
const countReducerAtom = atomWithReducer(0, countReducer)```
<CodeSandbox id="g3tsx" />## useReducerAtom
```jsximport { atom } from 'jotai'import { useReducerAtom } from 'jotai/utils'
const countReducer = (prev, action) => {  if (action.type === 'inc') return prev + 1  if (action.type === 'dec') return prev - 1  throw new Error('unknown action type')}
const countAtom = atom(0)
const Counter = () => {  const [count, dispatch] = useReducerAtom(countAtom, countReducer)  return (    <div>      {count}      <button onClick={() => dispatch({ type: 'inc' })}>+1</button>      <button onClick={() => dispatch({ type: 'dec' })}>-1</button>    </div>  )}```
<CodeSandbox id="eg0mw" />