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。以下是八种常用的 React Hooks，以及它们的概念、示例、横向对比和难点解析。
- useState
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>
);
}- useEffect
import React, { useState, useEffect } from 'react';
function Example() {
const [count, setCount] = useState(0);
// 类似于类中的componentDidMount和componentDidUpdate:
useEffect(() => {
// 更新文档的标题
document.title = `You clicked ${count} times`;
});
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>Click me</button>
</div>
);
}- useContext
import React, { useContext } from 'react';
import { ThemeContext } from './ThemeContext';
function Button() {
const theme = useContext(ThemeContext);
return (
<button style={{ background: theme.background, color: theme.foreground }}>
I am styled by theme context!
</button>
);
}- useReducer
import React, { useReducer } from 'react';
function Example() {
const [state, dispatch] = useReducer(reducer, initialState);
function handleIncrementClick() {
dispatch({ type: 'increment' });
}
return (
<div>
<p>Count: {state.count}</p>
<button onClick={handleIncrementClick}>Increment</button>
</div>
);
}
function reducer(state, action) {
switch (action.type) {
case 'increment':
return { count: state.count + 1 };
default:
throw new Error();
}
}- useCallback
import React, { useCallback } from 'react';
function Example() {
const memoizedCallback = useCallback(() => {
doSomething(a, b);
}, [a, b]);
return <SomeComponent onSomething={memoizedCallback} />;
}- useMemo
import React, { useMemo } from 'react';
function Example() {
const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);
return <div>{memoizedValue}</div>;
}- useRef
import React, { useRef } from 'react';
function Example() {
const ref = useRef(null);
function handleClick() {
ref.current.focus();
}
return (