Hey there, fellow UI developer! Are you ready to dive into the exciting world of React Hooks? If you've been working with React for a while, you might remember the days when class components were the go-to for managing state and side effects. But times have changed, and React Hooks have revolutionized the way we build components.
In this friendly guide, we'll explore 10 essential React Hooks, complete with example tutorials to help you understand and implement them in your projects. Whether you're new to Hooks or looking to deepen your knowledge, this post has got you covered. So, grab your favorite beverage, get comfortable, and let's embark on this React Hooks adventure together!
Let's kick things off with the most commonly used Hook: useState. This little gem allows you to add state to your functional components without the need for classes.
The useState Hook returns an array with two elements: the current state value and a function to update it. Here's a simple example:
import React, { useState } from 'react';
function Counter() {
const [count, setCount] = useState(0);
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}
In this example, we're creating a counter that increases every time the button is clicked. The useState Hook initializes our count to 0, and we use the setCount function to update it.
Next up is useEffect, the Hook that lets you perform side effects in your components. It's like componentDidMount, componentDidUpdate, and componentWillUnmount all rolled into one!
useEffect takes two arguments: a function to run after render, and an optional array of dependencies. Here's an example:
import React, { useState, useEffect } from 'react';
function WindowWidth() {
const [width, setWidth] = useState(window.innerWidth);
useEffect(() => {
const handleResize = () => setWidth(window.innerWidth);
window.addEventListener('resize', handleResize);
// Cleanup function
return () => {
window.removeEventListener('resize', handleResize);
};
}, []); // Empty dependency array means this effect runs once on mount
return <div>Window width: {width}px</div>;
}
In this example, we're using useEffect to add an event listener for window resizing. The cleanup function removes the listener when the component unmounts.
The useContext Hook provides a way to consume context in functional components without the need for render props or higher-order components.
First, you create a context using React.createContext(), then use the useContext Hook to consume it:
import React, { useContext } from 'react';
const ThemeContext = React.createContext('light');
function ThemedButton() {
const theme = useContext(ThemeContext);
return <button className={theme}>I'm styled by theme context!</button>;
}
function App() {
return (
<ThemeContext.Provider value="dark">
<ThemedButton />
</ThemeContext.Provider>
);
}
In this example, ThemedButton uses the useContext Hook to access the current theme value from ThemeContext.
When useState isn't enough, useReducer comes to the rescue. It's particularly useful for managing more complex state logic.
useReducer takes a reducer function and an initial state, and returns the current state paired with a dispatch method:
import React, { useReducer } from 'react';
const initialState = {count: 0};
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();
}
}
function Counter() {
const [state, dispatch] = useReducer(reducer, initialState);
return (
<>
Count: {state.count}
<button onClick={() => dispatch({type: 'decrement'})}>-</button>
<button onClick={() => dispatch({type: 'increment'})}>+</button>
</>
);
}
In this example, we're using useReducer to manage a counter with increment and decrement actions.
The useCallback Hook can help you optimize the performance of your components by memoizing callback functions.
useCallback returns a memoized version of the callback that only changes if one of the dependencies has changed:
import React, { useState, useCallback } from 'react';
function ParentComponent() {
const [count, setCount] = useState(0);
const increment = useCallback(() => {
setCount(c => c + 1);
}, []);
return (
<div>
<ChildComponent onIncrement={increment} />
<p>Count: {count}</p>
</div>
);
}
function ChildComponent({ onIncrement }) {
console.log('ChildComponent rendered');
return <button onClick={onIncrement}>Increment</button>;
}
In this example, the increment function is memoized with useCallback, preventing unnecessary re-renders of ChildComponent.
Similar to useCallback, useMemo is used for optimization, but it memoizes the result of a computation.
useMemo takes a function and an array of dependencies, and only recomputes the memoized value when one of the dependencies has changed:
import React, { useState, useMemo } from 'react';
function ExpensiveComponent({ list }) {
const [filter, setFilter] = useState('');
const filteredList = useMemo(() => {
console.log('Filtering list...');
return list.filter(item => item.toLowerCase().includes(filter.toLowerCase()));
}, [list, filter]);
return (
<div>
<input
type="text"
value={filter}
onChange={e => setFilter(e.target.value)}
placeholder="Filter list"
/>
<ul>
{filteredList.map(item => (
<li key={item}>{item}</li>
))}
</ul>
</div>
);
}
In this example, we're using useMemo to memoize the filtered list, preventing unnecessary recalculations on every render.
The useRef Hook provides a way to create a mutable reference that persists across re-renders.
useRef returns a mutable ref object whose .current property is initialized to the passed argument:
import React, { useRef, useEffect } from 'react';
function AutoFocusInput() {
const inputRef = useRef(null);
useEffect(() => {
inputRef.current.focus();
}, []);
return <input ref={inputRef} />;
}
In this example, we're using useRef to get a reference to the input element and focus it when the component mounts.
useImperativeHandle customizes the instance value that is exposed to parent components when using ref.
useImperativeHandle should be used with forwardRef:
import React, { useRef, useImperativeHandle, forwardRef } from 'react';
const FancyInput = forwardRef((props, ref) => {
const inputRef = useRef();
useImperativeHandle(ref, () => ({
focus: () => {
inputRef.current.focus();
},
getValue: () => {
return inputRef.current.value;
}
}));
return <input ref={inputRef} />;
});
function Parent() {
const fancyInputRef = useRef();
const handleClick = () => {
fancyInputRef.current.focus();
console.log(fancyInputRef.current.getValue());
};
return (
<div>
<FancyInput ref={fancyInputRef} />
<button onClick={handleClick}>Focus Input</button>
</div>
);
}
In this example, we're using useImperativeHandle to customize what instance value is exposed to the parent component.
useLayoutEffect is similar to useEffect, but it fires synchronously after all DOM mutations.
The signature is identical to useEffect, but it fires synchronously before the browser has a chance to paint:
import React, { useState, useLayoutEffect } from 'react';
function Tooltip() {
const [tooltipHeight, setTooltipHeight] = useState(0);
const tooltipRef = useRef();
useLayoutEffect(() => {
const height = tooltipRef.current.clientHeight;
setTooltipHeight(height);
}, []);
return (
<div>
<div ref={tooltipRef}>Tooltip content</div>
<p>The tooltip height is: {tooltipHeight}px</p>
</div>
);
}
In this example, we're using useLayoutEffect to measure the height of a DOM element synchronously before the browser paints.
Last but not least, useDebugValue can be used to display a label for custom hooks in React DevTools.
useDebugValue accepts a value and an optional formatting function:
import React, { useState, useDebugValue } from 'react';
function useFriendStatus(friendID) {
const [isOnline, setIsOnline] = useState(null);
// ... Logic to determine if the friend is online ...
useDebugValue(isOnline ? 'Online' : 'Offline');
return isOnline;
}
function FriendListItem(props) {
const isOnline = useFriendStatus(props.friend.id);
return (
<li style={{ color: isOnline ? 'green' : 'black' }}>
{props.friend.name}
</li>
);
}
In this example, we're using useDebugValue to display the friend's online status in React DevTools.
Wow, we've covered a lot of ground! From managing state with useState to optimizing performance with useMemo and useCallback, React Hooks offer a powerful and flexible way to build UI components. Let's recap the 10 Hooks we've explored:
Remember, the key to mastering React Hooks is practice. Start by incorporating them into your projects one at a time. As you become more comfortable, you'll find that Hooks can significantly simplify your code and make your components more reusable and easier to understand.
不要害怕嘗試和組合不同的 Hook 來解決複雜的問題。 React 社群不斷提出新的模式和自訂 Hook，因此請繼續學習並分享您的發現！
我希望這個友善的指南能夠幫助您更好地掌握 React Hooks。祝您編碼愉快，並祝福您的組件永遠功能齊全且精彩！
「Hooks 是 React 16.8 中的新增功能。它們讓您無需編寫類別即可使用狀態和其他 React 功能。」- React 文件
現在就去連接吧！ ??
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