react性能优化之useMemo,useCallback的使用

//useMemo,useCallback
import React, { memo, useMemo, useCallback, useState } from 'react';
// import About from './About';

const Foo = memo((props) => {
  let count = props.count;
  console.log("函数重新渲染");
  return <div onClick={props.addCount}>count:{count}</div>
});

// class App extends PureComponent {
//   state = {
//     count: 0,
//     name: 0
//   }
//   render() {
//     return (
//       <Fragment>
//         <Foo count={this.state.count} ></Foo>
//         <button onClick={() => { this.setState(() => ({ count: this.state.count + 1 })) }}>加count</button>
//       </Fragment>
//     )
//   }
// }
const App = memo(() => {
  const [count, setCount] = useState(0);
  let double = useMemo(() => {
    return count * 2
  }, [count==3]);
  let addCount=useCallback(()=>{    //useCallback 可以看成useMemo返回函数时的简写，赋值给onClick 不会引发函数重新渲染
    setCount((count) => count + 1)
  },[]);  //括号可以看成依赖数组，当为空时，只有第一次挂载时才会渲染，当有数据时如[count]，当count改变时才会改变，有多个数据时，所有数据改变时才会改变
  // const addCount=()=>{
  //   setCount((count) => count + 1)
  // }
  return (
    <div>
      <Foo addCount={addCount} count={double}></Foo>
      <button onClick={()=>{setCount((count) => count + 1)}}>count+1</button>   //直接赋值当数据改变时，这个函数会重复渲染浪费性能
　　　　<button onClick={addCount}>count+1<button>
   </div>
  )
})
export default App;

标签：count,return,useMemo,setCount,useCallback,react,const
来源： https://www.cnblogs.com/uimeigui/p/12655619.html