28.说说你对useReducer的理解#

import { useReducer } from "react";

const defaultvalue={
  count:0
}

const reducer = (state, action) => {
  switch (action.type) {
    case 'increment':
      return {
        count: state.count + 1,
      }
      case 'decrement':
        return {
          count: state.count - 1,
        }
    default:
      throw new Error(`Unknown action type "${action.type}"`)
  }
}

function App() {
  const [state,dispatch]=useReducer(reducer,defaultvalue)
  const increment = () => {
    dispatch({
      type:'increment',
    })
  }
  const decrement = () => {
    dispatch({
      type:'decrement',
    })
  }

  return (
    <div>
      <p>{state.count}</p>
      <button onClick={increment}>increment</button>
      <button onClick={decrement}>decrement</button>
    </div>
  )
}

export default App;