react总结之hooks

React Hooks 是 React 16.8 的新增特性，它可以让你在函数组件中使用 state 以及其他的 React 特性，而无需编写 class。

以下是一些常用的 React Hooks 的例子：

1. useState: 用于添加函数组件的 state。

import React, { useState } from 'react';
 
function Example() {
  const [count, setCount] = useState(0);
  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

2. useEffect: 用于处理副作用。

import React, { useState, useEffect } from 'react';
 
function Example() {
  const [count, setCount] = useState(0);
 
  // 类似于 class 组件的生命周期函数 componentDidMount 和 componentDidUpdate:
  useEffect(() => {
    // 更新 document 的 title
    document.title = `You clicked ${count} times`;
  });
 
  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

3. useContext: 用于访问 context。

import React, { useContext } from 'react';
import { ThemeContext } from './ThemeContext';
 
function Button() {
  const theme = useContext(ThemeContext);
  return (
    <button style={{ backgroundColor: theme.background }}>
      I am styled by theme context!
    </button>
  );
}

4. useReducer: 用于管理复杂的 state 逻辑。

import React, { useReducer } from 'react';
 
function Example() {
  const [state, dispatch] = useReducer(reducer, initialState);
 
  function reducer(state, action) {
    switch (action.type) {
      case 'increment':
        return {count: state.count + 1};
      case 'decrement':
        return {count: state.count - 1};
      default:
        throw new Error();
    }
  }
 
  return (
    <>
      Count: {state.count}
      <button onClick={() => dispatch({type: 'increment'})}>+</button>
      <button onClick={() => dispatch({type: 'decrement'})}>-</button>
    </>
  );
}

5. useCallback: 用于记住 callback 函数的变化。

import React, { useCallback } from 'react';
 
function Example() {
  const memoizedCallback = useCallback(
    () => {
      doSomething(a, b);
    },
    [a, b],
  );
 
  return <button onClick={memoizedCallback}>Click me</button>;
}

6. useMemo: 用于记住计算结果的变化。

import React, { useMemo } from 'react';
 
function Example() {
  const mem