React has been a game-changer in the world of web development. It’s time to explore the exciting world of hooks. React introduces a plethora of hooks to simplify your component logic, making your code more efficient and maintainable. In this article, we’ll delve into 15 new hooks that come with React 18, explaining their usage and providing real-world examples.
| No. | React Hook |
|---|---|
| 1. | useState |
| 2. | useReducer |
| 3. | useContext |
| 4. | useEffect |
| 5. | useLayoutEffect |
| 6. | useDebugValue |
| 7. | useRef |
| 8. | useImperativeHandle |
| 9. | useCallback |
| 10. | useMemo |
| 11. | useLocation |
| 12. | useHistory |
| 13. | useParams |
| 14. | useTransition |
| 15. | useDeferredValue |
| 16. | custom hooks |
useState is one of the most commonly used React hooks, introduced in React 16.8. It allows functional components to manage and update their internal state, making them dynamic and responsive. With useState, you can declare state variables and easily update them, triggering re-renders when the state changes.
Example of useState in React
Here’s a simple example of how to use useState in a React functional component:
import React, { useState } from 'react';
function Counter() {
// Declare a state variable named "count" with an initial value of 0
const [count, setCount] = useState(0);
// Event handler to increment the count
const incrementCount = () => {
setCount(count + 1);
};
// Event handler to reset the count
const resetCount = () => {
setCount(0);
};
return (
<div>
<p>Count: {count}</p>
<button onClick={incrementCount}>Increment</button>
<button onClick={resetCount}>Reset</button>
</div>
);
}
export default Counter;
In this example, we create a Counter component using the useState hook. Here’s a breakdown of what’s happening:
We import React and the useState hook from the ‘react’ library.
Inside the Counter component, we declare a state variable named count using the useState hook. The initial value of count is set to 0. The useState function returns an array with two elements: the current state value (count) and a function to update that state (setCount).
We define two event handlers, incrementCount and resetCount, which use the setCount function to update the count state. When setCount is called, it triggers a re-render of the component with the new state value.
In the component’s JSX, we display the current count value, and there are two buttons. Clicking the “Increment” button calls the incrementCount function, and clicking the “Reset” button calls the resetCount function, updating the count accordingly.
The useState hook simplifies state management in functional components, making it easy to handle and update component-specific data. It allows you to create interactive and dynamic user interfaces without the need for class components or complex state management code.
useReducer is a React hook that is used to manage state in a more structured and predictable way. It is especially useful when you have state that depends on the previous state and when you need to handle complex state transitions and logic.
Example of useReducer in React
Here’s an example of how to use useReducer in a React functional component:
import React, { useReducer } from 'react';
// Define a reducer function
function counterReducer(state, action) {
switch (action.type) {
case 'increment':
return { count: state.count + 1 };
case 'decrement':
return { count: state.count - 1 };
default:
return state;
}
}
function Counter() {
const [state, dispatch] = useReducer(counterReducer, { count: 0 });
return (
<div>
<p>Count: {state.count}</p>
<button onClick={() => dispatch({ type: 'increment' })}>Increment</button>
<button onClick={() => dispatch({ type: 'decrement' })}>Decrement</button>
</div>
);
}
export default Counter;
In this example, we create a counter component using the useReducer hook. The counterReducer function defines how the state should be updated based on different actions, and the dispatch function is used to dispatch these actions.
State Hooks, whether useState or useReducer, have transformed the way we handle state in React. They have brought simplicity, clarity, and reusability to state management, making React applications more efficient and maintainable.
In this article, we’ll explore these hooks in greater depth, provide examples of their usage, and discuss best practices to help you become proficient in managing state in your React applications.
useContext is a React hook that allows functional components to access context values. Context in React is a way to share data that can be considered “global” to a component tree, without manually passing it through props at each level.
Example of useContext in React
In this example, we'll create a simple theme-switching application that uses `useContext` to share the current theme throughout the component tree.
Step 1: Create a Theme Context
First, define a theme context with an initial theme value:
// ThemeContext.js
import React, { createContext, useContext, useState } from 'react';
const ThemeContext = createContext();
export function ThemeProvider({ children }) {
const [theme, setTheme] = useState('light');
const toggleTheme = () => {
setTheme(theme === 'light' ? 'dark' : 'light');
};
return (
<ThemeContext.Provider value=>
{children}
</ThemeContext.Provider>
);
}
export function useTheme() {
return useContext(ThemeContext);
}
In this code:
- We create a `ThemeContext` using the `createContext` function. - We define a `ThemeProvider` component that manages the theme state and provides the theme value and a function to toggle the theme using the `useState` hook. - The `useTheme` custom hook allows us to easily access the theme and toggle function.
Step 2: Using useContext to Consume the Context
Now, let’s use the theme context in our components:
// App.js
import React from 'react';
import { ThemeProvider, useTheme } from './ThemeContext';
import ThemeSwitcher from './ThemeSwitcher';
function App() {
return (
<ThemeProvider>
<div className="App">
<Header />
<Content />
</div>
</ThemeProvider>
);
}
function Header() {
const { theme } = useTheme();
return (
<header className={`header ${theme}`}>
<h1>My Theme App</h1>
<ThemeSwitcher />
</header>
);
}
function Content() {
const { theme } = useTheme();
return (
<div className={`content ${theme}`}>
<p>This is the content of my app.</p>
</div>
);
}
export default App;
In this code:
App component with the ThemeProvider, which provides the theme context.Header and Content components, we use the useTheme custom hook to access the theme value.className of the elements, allowing us to switch between “light” and “dark” themes.Step 3: Create the ThemeSwitcher Component
Let’s create a component to switch between themes:
// ThemeSwitcher.js
import React from 'react';
import { useTheme } from './ThemeContext';
function ThemeSwitcher() {
const { theme, toggleTheme } = useTheme();
return (
<button onClick={toggleTheme}>
Switch to {theme === 'light' ? 'dark' : 'light'} mode
</button>
);
}
export default ThemeSwitcher;
In this component, we use the useTheme custom hook to access the theme and toggleTheme function to switch between light and dark themes.
By using the useContext hook along with a custom hook, you can efficiently access and manage shared state or data within your React application without the need for prop drilling, making your code more maintainable and clean.
useEffect is a React Hook that allows you to perform side effects in functional components. It’s equivalent to the lifecycle methods componentDidMount, componentDidUpdate, and componentWillUnmount in class components. With useEffect, you can execute code after the component has rendered and react to changes in props and state.
Example of useEffect in React
In this example, we’ll create a simple React component that fetches and displays data from an API when the component is mounted.
import React, { useState, useEffect } from 'react';
function DataFetchingComponent() {
const [data, setData] = useState([]);
const [loading, setLoading] = useState(true);
useEffect(() => {
// This code block runs after the component has rendered
fetch('https://api.example.com/data') // Replace with your API endpoint
.then((response) => response.json())
.then((result) => {
setData(result);
setLoading(false);
})
.catch((error) => {
console.error('Error fetching data: ', error);
setLoading(false);
});
}, []); // The empty dependency array means this effect runs only on component mount
return (
<div>
{loading ? (
<p>Loading...</p>
) : (
<ul>
{data.map((item) => (
<li key={item.id}>{item.name}</li>
))}
</ul>
)}
</div>
);
}
export default DataFetchingComponent;
In this code:
useState, and useEffect from ‘react’.DataFetchingComponent.data and loading using the useState hook.useEffect hook to fetch data from an API when the component is mounted. The empty dependency array [] indicates that this effect should only run once after the initial render.Here’s a step-by-step explanation of what’s happening:
When the component is mounted, the useEffect code block fetches data from the API using the fetch function.
Once the data is fetched, it’s processed, and the state is updated using the setData and setLoading functions, which triggers a re-render.
3. The component renders either a “Loading…” message or a list of data items based on the loading state.
Using useEffect, you can easily manage asynchronous operations, data fetching, and other side effects within your functional components. It helps keep your components clean, efficient, and responsive to changes.
useLayoutEffect is a React Hook that is similar to useEffect. The key difference is the timing of when the effect runs. useLayoutEffect runs synchronously after the DOM is mutated but before the browser repaints. This makes it ideal for tasks that require immediate DOM changes.
Example of useLayoutEffect in React
In this example, we’ll create a React component that uses useLayoutEffect to change the background color of a button element immediately after it’s rendered. This demonstrates how useLayoutEffect can be useful for tasks that require changes to the DOM before it’s painted.
import React, { useState, useLayoutEffect } from 'react';
function ButtonComponent() {
const [backgroundColor, setBackgroundColor] = useState('white');
useLayoutEffect(() => {
setBackgroundColor('blue'); // Change the background color immediately after rendering
}, []); // The empty dependency array means this effect runs only once after the initial render
return (
<button style=>Click me</button>
);
}
export default ButtonComponent;
In this code:
useState, and useLayoutEffect from ‘react’.ButtonComponent.backgroundColor using the useState hook.The key part is the useLayoutEffect:
The useLayoutEffect code block changes the backgroundColor state variable to ‘blue’ immediately after rendering, thanks to the synchronous nature of useLayoutEffect.
The component renders a button element with a dynamic background color based on the backgroundColor state.
When the component is rendered, the button’s background color changes to ‘blue’ without waiting for the next browser paint. This demonstrates how useLayoutEffect can be useful for tasks that require immediate DOM changes, ensuring a smoother user experience.
Keep in mind that, in most cases, you’ll use the standard useEffect hook for handling side effects, as it doesn’t block the painting phase. useLayoutEffect is generally used for very specific scenarios where synchronous DOM mutations are required.
useDebugValue is a hook that enables you to provide additional information about your custom hooks for React DevTools. It’s particularly useful when creating custom hooks that encapsulate complex logic or state management, making it easier to understand and debug the behavior of these hooks.
Example of useDebugValue in a Custom Hook
In this example, we’ll create a simple custom hook called useCounter that counts and displays a value. We’ll use useDebugValue to provide a label for React DevTools.
import { useState, useEffect, useDebugValue } from 'react';
function useCounter(initialValue) {
const [count, setCount] = useState(initialValue);
useEffect(() => {
document.title = `Count: ${count}`;
}, [count]);
useDebugValue(count, (count) => `Custom Counter: ${count}`); // Debug label
return { count, increment: () => setCount(count + 1) };
}
export default useCounter;
In this code:
We import React’s useState, useEffect, and useDebugValue hooks.
We create a custom hook named useCounter that takes an initial value and returns an object with the current count value and an increment function to increase the count.
Inside the useEffect, we update the document title with the current count whenever the count changes.
The key part is the useDebugValue hook. We use it to provide a label and value for React DevTools. This allows you to see a more informative label in DevTools when inspecting this custom hook. The custom label is created based on the count value.
Using the useCounter custom hook
Now, you can use the useCounter custom hook in your components:
import React from 'react';
import useCounter from './useCounter';
function CounterComponent() {
const counter = useCounter(0);
return (
<div>
<p>Count: {counter.count}</p>
<button onClick={counter.increment}>Increment</button>
</div>
);
}
export default CounterComponent;
In this component, we use the useCounter custom hook to manage the count state and increment function. The custom label provided by useDebugValue will be visible in React DevTools when inspecting the useCounter hook.
This example demonstrates how useDebugValue can be used to improve the debugging experience when creating custom hooks by providing informative labels for custom hooks in React DevTools. It’s especially helpful for hooks that encapsulate complex logic or state management.
useRef is a Hook that provides a way to reference and interact with DOM elements and other values in a functional component. It is commonly used when you need to access the underlying DOM, manage values that don’t trigger re-renders, or perform actions that require direct manipulation.
Example of useRef in React
In this example, we’ll use useRef to focus an input element when the component mounts:
import React, { useRef, useEffect } from 'react';
function FocusInput() {
// Create a ref to store a reference to the input element
const inputRef = useRef(null);
// Use useEffect to focus the input element when the component mounts
useEffect(() => {
inputRef.current.focus();
}, []);
return (
<div>
<p>Click the button to focus the input field:</p>
<input ref={inputRef} />
</div>
);
}
export default FocusInput;
In this code:
We import React, useRef, and useEffect from ‘react’.
Inside the FocusInput component, we create a ref using useRef. The initial value of the ref is set to null.
We use the useEffect hook to focus the input element when the component mounts. We do this by calling inputRef.current.focus().
In the component’s JSX, we render a paragraph and an input field. We attach the inputRef to the ref attribute of the input element.
When the component mounts, the useEffect is triggered, and it calls inputRef.current.focus(), which focuses the input field.
This is just a basic example of how to use useRef to access and interact with DOM elements. You can also use useRef to store and manipulate values, including custom data, without causing re-renders in your component. useRef is a versatile tool for handling various scenarios in React.
useImperativeHandle is a Hook that gives you control over what is exposed when a parent component uses a ref to access a child component. It allows you to customize the instance value that the parent component sees, making it possible to expose only the methods or properties that are relevant.
Example of useImperativeHandle in React
Child Component (Child.js):
import React, { useImperativeHandle, forwardRef } from 'react';
const Child = forwardRef((props, ref) => {
// Create a local variable
let count = 0;
// Define a function that increments the count
const incrementCount = () => {
count += 1;
};
// Expose the incrementCount function to the parent component
useImperativeHandle(ref, () => ({
incrementCount,
}));
return (
<div>
<p>Child Component</p>
</div>
);
});
export default Child;
In this code:
We import React, useImperativeHandle, and forwardRef from ‘react’.
We create a functional child component called Child.
Inside the Child component, we define a local variable count and a function incrementCount that increments the count.
We use useImperativeHandle to expose the incrementCount function to the parent component via the ref. This means the parent can access and call the incrementCount function on the child component.
Parent Component (Parent.js):
import React, { useRef } from 'react';
import Child from './Child';
function Parent() {
const childRef = useRef();
const handleIncrement = () => {
childRef.current.incrementCount();
};
return (
<div>
<p>Parent Component</p>
<button onClick={handleIncrement}>Increment Child Count</button>
<Child ref={childRef} />
</div>
);
}
export default Parent;
In this code:
We create a parent component called Parent.
Inside the Parent component, we use useRef to create a childRef that we will use to access the child component.
We define a function handleIncrement that calls the incrementCount function on the child component when a button is clicked.
The Child component is rendered with a ref attribute that points to the childRef. This allows the parent to access the child component and call the incrementCount function.
When you click the “Increment Child Count” button in the parent component, it calls the incrementCount function in the child component, incrementing the count variable in the child. This demonstrates how useImperativeHandle allows you to expose specific methods or properties of a child component to its parent, providing greater control and encapsulation of functionality.
useCallback is a React Hook that memoizes a function, creating a memoized version of the function that will only change if its dependencies change. This is beneficial when you want to optimize performance by avoiding re-creating functions on each render, especially when those functions are passed as props to child components.
Example of useCallback in React
In this example, we’ll create a simple counter application with two buttons, and we’ll use useCallback to optimize the event handler functions.
import React, { useState, useCallback } from 'react';
function Counter() {
const [count, setCount] = useState(0);
// Create memoized event handlers with useCallback
const increment = useCallback(() => {
setCount(count + 1);
}, [count]);
const decrement = useCallback(() => {
setCount(count - 1);
}, [count]);
return (
<div>
<p>Count: {count}</p>
<button onClick={increment}>Increment</button>
<button onClick={decrement}>Decrement</button>
</div>
);
}
export default Counter;
In this code:
We import React, useState, and useCallback from ‘react’.
Inside the Counter component, we declare a state variable count to hold the current count and an event handler function setCount to update the count.
We create two memoized event handlers, increment and decrement, using useCallback. These event handlers update the count state by incrementing and decrementing it, respectively.
We provide the useCallback hook with a dependency array. In this case, the dependency array contains the count variable, which indicates that the event handlers should only be recreated if the count value changes.
In the component’s JSX, we display the current count and two buttons with the memoized event handlers for increment and decrement.
By using useCallback, the event handlers are memoized and only recreated when the count variable changes. This optimization prevents unnecessary re-renders and can be especially useful in scenarios where you pass these functions as props to child components. It helps improve the performance of your React applications by ensuring that functions remain consistent and do not cause unnecessary re-renders.
useMemo is a React Hook that memoizes a value based on a function and a list of dependencies. It calculates the value once and then returns that memoized value on subsequent renders unless one of the dependencies has changed. This can be particularly useful when you need to optimize the calculation of derived data, heavy computations, or data transformations.
Example of useMemo in React
In this example, we’ll create a simple React component that calculates the factorial of a number using useMemo to optimize the computation:
import React, { useState, useMemo } from 'react';
function FactorialCalculator({ number }) {
const factorial = useMemo(() => calculateFactorial(number), [number]);
function calculateFactorial(n) {
if (n === 0 || n === 1) {
return 1;
}
return n * calculateFactorial(n - 1);
}
return (
<div>
<p>Factorial of {number} is {factorial}</p>
</div>
);
}
export default FactorialCalculator;
In this code:
We import React, useState, and useMemo from ‘react’.
Inside the FactorialCalculator component, we receive a number prop, which is the input for which we want to calculate the factorial.
We use the useMemo hook to memoize the result of the calculateFactorial function. The first argument to useMemo is a function that performs the calculation, and the second argument is an array of dependencies. In this case, the dependency is the number prop. The value is calculated only when the number prop changes.
The calculateFactorial function is a recursive function that calculates the factorial of a number.
In the component’s JSX, we display the calculated factorial.
By using useMemo, we ensure that the factorial value is calculated only when the number prop changes. If the number prop remains the same between renders, the memoized factorial value is reused, preventing unnecessary re-computation and improving the performance of the component.
useMemo is especially valuable when you have expensive computations or data transformations in your components. It optimizes your application by ensuring that calculations are performed only when necessary and reusing previously calculated results when the dependencies don’t change.
The useLocation hook is commonly used in React applications that use the react-router-dom library for client-side routing. It provides access to the current location object, allowing you to examine and work with the various parts of the URL, such as the pathname and search parameters. This is useful for creating dynamic UIs and navigation based on the current URL.
Example of useLocation in React
Suppose you have a React application that uses react-router-dom for routing. Here’s how you can use the useLocation hook to access and display the current pathname and search parameters in your component:
First, make sure to install react-router-dom if you haven’t already:
npm install react-router-dom
Now, let’s create a simple component that uses the useLocation hook:
import React from 'react';
import { useLocation } from 'react-router-dom';
function CurrentLocation() {
// Use the useLocation hook to access the current location object
const location = useLocation();
return (
<div>
<h2>Current Location Details:</h2>
<p>Pathname: {location.pathname}</p>
<p>Search Params: {location.search}</p>
</div>
);
}
export default CurrentLocation;
In this example:
We import useLocation from 'react-router-dom'.
Inside the CurrentLocation component, we use the useLocation hook to access the current location object, which contains information about the URL.
We then display the current pathname and search parameters from the location object in the component.
Remember to use this component within a Router context provided by react-router-dom so that the useLocation hook can access the current route information. When the route changes, the CurrentLocation component will automatically reflect the updated URL information.
This is just a simple example, but you can use the useLocation hook to create more complex navigation and UI features based on the current URL in your React application.
The useHistory hook is part of the react-router-dom library and provides a way to interact with the browser’s history and navigate between routes programmatically in a React application. It’s particularly useful for implementing dynamic navigation, redirecting users, and performing actions based on user interactions.
Example of useHistory in React
Suppose you have a simple React application that uses react-router-dom for routing. Here’s how you can use the useHistory hook to programmatically navigate to different routes based on user interactions:
First, ensure you have react-router-dom installed:
npm install react-router-dom
Now, let’s create a component that uses the useHistory hook:
import React from 'react';
import { useHistory } from 'react-router-dom';
function NavigationExample() {
// Use the useHistory hook to get access to the history object
const history = useHistory();
const navigateToAbout = () => {
// Programmatically navigate to the '/about' route
history.push('/about');
};
const goBack = () => {
// Navigate back in the browser's history
history.goBack();
};
return (
<div>
<h2>Navigation Example</h2>
<button onClick={navigateToAbout}>Go to About</button>
<button onClick={goBack}>Go Back</button>
</div>
);
}
export default NavigationExample;
In this example:
We import useHistory from 'react-router-dom'.
Inside the NavigationExample component, we use the useHistory hook to get access to the history object.
We define two functions: navigateToAbout and goBack. When the buttons are clicked, these functions use the history object to perform navigation actions.
navigateToAbout uses history.push('/about') to programmatically navigate to the ‘/about’ route.
goBack uses history.goBack() to navigate back in the browser’s history stack.
Make sure that this component is used within a Router context provided by react-router-dom to access the history object properly. The useHistory hook allows you to create dynamic and interactive navigation elements in your React application.
The useParams hook is part of the react-router-dom library and provides a way to access URL parameters defined in your routes. URL parameters are placeholders in your route patterns that can capture dynamic values from the URL and make them available in your components. This is useful for building components that rely on dynamic data from the URL.
Example of useParams in React
Suppose you have a React application with a route that includes a dynamic URL parameter, such as a product ID. You can use the useParams hook to access and use that parameter in your component:
First, ensure you have react-router-dom installed:
npm install react-router-dom
```
Now, let's create a component that uses the `useParams` hook:
```javascript
import React from 'react';
import { useParams } from 'react-router-dom';
function ProductDetail() {
// Use the useParams hook to access URL parameters
const { productId } = useParams();
return (
<div>
<h2>Product Detail</h2>
<p>Product ID: {productId}</p>
</div>
);
}
export default ProductDetail;
```
In this example:
- We import `useParams` from `'react-router-dom'`.
- Inside the `ProductDetail` component, we use the `useParams` hook to access URL parameters. In this case, we're capturing the `productId` parameter from the URL.
- We display the value of the `productId` parameter in the component, allowing you to use it for data retrieval, rendering, or any other purpose.
To use this component and see it in action, you would define a route in your routing configuration that includes a dynamic URL parameter, like this:
```javascript
import { BrowserRouter, Route, Switch } from 'react-router-dom';
function App() {
return (
<BrowserRouter>
<Switch>
<Route path="/products/:productId">
<ProductDetail />
</Route>
</Switch>
</BrowserRouter>
);
}
```
In this route configuration, the `:productId` part of the route pattern captures the dynamic product ID from the URL. The `ProductDetail` component can then access and use this ID via the `useParams` hook.
Using the `useParams` hook in combination with dynamic routes allows you to create components that adapt to different URL parameters and provide dynamic content based on the current route.
**[🔝 Back to Top](#table-of-contents)**
In React 18’s concurrent mode, the useTransition function is used to handle the transition between different render states. Concurrent mode allows React to work on multiple tasks concurrently, making applications more responsive and efficient.
The useTransition function is typically used to wrap asynchronous operations, such as data fetching, to provide a smoother user experience. It helps manage the transition between loading and rendering data by allowing you to show loading indicators or placeholders while data is being fetched, and then smoothly transitioning to the actual data when it’s ready.
Example of useTransition in React
Here’s a conceptual example of how useTransition might be used in a React 18 application, although please note that this example does not reflect the actual API (as of my last update) but illustrates the concept:
import React, { useTransition } from 'react';
function AsyncDataFetchingComponent() {
const [startTransition, isPending] = useTransition();
const fetchData = async () => {
startTransition(() => {
// While fetching data, you can show a loading indicator or placeholder.
// React will manage the transition smoothly.
fetch('https://api.example.com/data')
.then((response) => response.json())
.then((data) => {
// Update the component state with the fetched data.
// React will transition to displaying the data.
});
});
};
return (
<div>
<button onClick={fetchData}>Fetch Data</button>
{isPending ? <LoadingIndicator /> : <DataDisplay />}
</div>
);
}
In this conceptual example:
We use the useTransition hook to start a transition.
When fetching data, React can show a loading indicator (LoadingIndicator) while transitioning to the data display (DataDisplay) when it’s ready.
It’s important to recognize that the example provided here is a simplified concept. In practice, utilizing useTransition and concurrent mode in React 18 may necessitate more intricate implementation and considerations. To ensure you are following the most current and effective practices, it is advisable to consult the latest React documentation and available resources.
The useDeferredValue hook is designed to manage when a value is transitioned from being “deferred” to being “current.” In React’s concurrent mode, when you have expensive or non-urgent data or computations, you can defer their processing to avoid blocking the main thread. This can lead to a more responsive user interface.
useDeferredValue is often used in combination with useTransition. You can specify which data should be deferred and when it should become “current,” allowing React to optimize the timing of rendering and transitions.
Example of useDeferredValue in React
Here’s a simplified example of how useDeferredValue might be used, although it should be considered a conceptual representation:
import React, { useDeferredValue, useTransition } from 'react';
function DeferredDataComponent() {
const [isPending, startTransition] = useTransition();
// Simulate expensive data fetching (replace with actual asynchronous operation)
const fetchData = async () => {
startTransition(() => {
// Deferring the processing of data
const deferredData = someExpensiveDataProcessing();
// Declare which data should be deferred
const deferredValue = useDeferredValue(deferredData);
// React will optimize when to make deferredValue "current"
// based on the rendering and transition priorities.
});
};
return (
<div>
<button onClick={fetchData}>Fetch Data</button>
{isPending ? <LoadingIndicator /> : <DataDisplay />}
</div>
);
}
In this conceptual example:
We use useDeferredValue to indicate that the deferredData should be transitioned to a “current” state when it’s appropriate according to React’s concurrent mode logic.
We use useTransition to manage the transition and indicate that some part of the rendering is pending.
While data is being processed, we can show a loading indicator (LoadingIndicator) and transition smoothly to the data display (DataDisplay) when the data becomes “current.”
Please note that this example is a simplified illustration of the concept of useDeferredValue. The actual use and behavior of useDeferredValue may be more complex and require consideration of concurrent mode principles. For the most accurate and up-to-date information on useDeferredValue and concurrent mode, refer to the latest React documentation and resources.
A custom hook is a JavaScript function that uses built-in hooks or other custom hooks to manage and share stateful logic. Custom hooks are typically used to abstract complex behavior or state management so that it can be reused across multiple components. They follow a naming convention with the “use” prefix to indicate that they are hooks.
Custom hooks can be used for a variety of purposes, such as data fetching, form handling, managing local storage, or any other functionality that involves state or side effects. They help keep components clean and focused by extracting logic into separate, reusable functions.
Example of a Custom Hook
import { useState, useEffect } from 'react';
function useWindowDimensions() {
const [windowDimensions, setWindowDimensions] = useState({
width: window.innerWidth,
height: window.innerHeight,
});
useEffect(() => {
function handleResize() {
setWindowDimensions({
width: window.innerWidth,
height: window.innerHeight,
});
}
window.addEventListener('resize', handleResize);
return () => {
window.removeEventListener('resize', handleResize);
};
}, []);
return windowDimensions;
}
export default useWindowDimensions;
In this code:
We create a custom useWindowDimensions hook that uses useState to manage the window dimensions (width and height).
We use useEffect to add a resize event listener that updates the window dimensions when the window is resized.
The hook returns the current window dimensions.
By using this custom hook, you can access and respond to window dimensions in your components to create responsive and dynamic layouts.
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