Hooks - useReducer

useReducer 可以做状态的一个转换

它接收两个参数，一个是参数的状态，一个参数是控制状态的

import React, { useReducer } from 'react';

function Example() {
   const [count, dispatch] = useReducer((state, action) => {
       switch(action) {
           case "add":
               return state + 1;
            case "sub":
                return state - 1;
            default:
                return state;
       }
   },0);

   return (
       <div>
           <p>this is {count}</p>
           <button onClick={() => dispatch("add")}>Increment</button>
           <button onClick={() => dispatch("sub")}>Decrement</button>
       </div>
   )
}

export default Example;