UseEffect is a fundamental hook in React that allows developers to perform side effects in functional components. Introduced with React 16.8, it serves as a replacement for lifecycle methods like componentDidMount and componentDidUpdate in class components. The primary purpose of UseEffect is to manage side effects such as data fetching, timers, and direct DOM manipulations.
UseEffect accepts two parameters: a callback function and a dependency array. The callback function is executed based on the dependencies specified. If the dependency array is empty, the callback is executed once when the component mounts. If dependencies are provided, the callback runs whenever one of these dependencies changes. This behavior allows developers to control when the side effects are triggered, ensuring efficient component updates.
Why UseEffect is Essential
UseEffect is crucial because it allows side effects to be handled outside of the component's rendering cycle. Placing side effects in the component body can lead to unnecessary re-renders, which degrade performance. By using UseEffect, developers can ensure that side effects are executed only when necessary, avoiding redundant calls.
This hook is particularly useful for data fetching. For instance, when fetching articles from an API, UseEffect can be set to run once upon component mount or whenever a category ID changes. This ensures that new data is fetched only when needed, optimizing both performance and user experience.
Asynchronous Nature of UseEffect
UseEffect executes its callback asynchronously. This design choice allows the browser to render the UI before executing the side effects, providing a smoother user experience. The asynchronous execution is managed using JavaScript's event loop, specifically through the task queue.
React uses a mechanism called MessageChannel, which helps ensure that the callback runs after the browser paints the UI. This approach prevents the main thread from being blocked, allowing users to see loading indicators or partial UI updates while data is being fetched in the background.
Common Mistakes and How to Avoid Them
One common issue with UseEffect is the infamous "nasty loop," where a component repeatedly re-renders due to a state change that triggers the effect. This often occurs when a state variable affecting the dependency array is updated within the UseEffect callback. To avoid this, make sure dependencies are correctly set and avoid updating state variables that are dependencies within the effect.
Another mistake is using async functions directly within UseEffect. Since async functions return a promise, they can interfere with the cleanup process of UseEffect. To fix this, wrap the async logic within a separate function and call it inside the UseEffect callback.
UseEffect vs. UseLayoutEffect
While UseEffect is asynchronous, React also provides UseLayoutEffect, which is a synchronous version. UseLayoutEffect runs before the browser paints the UI, making it suitable for operations that require immediate updates before the UI is visible to the user.
UseLayoutEffect is useful when you need to measure DOM elements or perform operations that require the DOM to be fully updated before executing. However, it should be used sparingly to avoid blocking the main thread and negatively impacting performance.
Handling Race Conditions and Cleanup
Race conditions can occur when fetching data if a user rapidly changes categories or navigates away from a page. To manage this, implement a cleanup function within UseEffect. This function can cancel ongoing requests using AbortController or other mechanisms, ensuring that users only see the most recent data.
Additionally, always clean up side effects like event listeners or timers. Failing to do so can lead to memory leaks and unexpected behavior when components are unmounted.
Optimizing Performance with Memoization
To reduce unnecessary re-renders, consider using useMemo alongside UseEffect. useMemo allows you to memoize values, ensuring that expensive calculations are only re-computed when necessary. This can be particularly useful for filtering data or complex computations that depend on specific state changes.
By using useMemo, you can avoid the delays introduced by UseEffect's asynchronous nature and improve the overall performance and responsiveness of your application.
Conclusion
Mastering UseEffect involves understanding its asynchronous execution, managing dependencies carefully, and handling side effects efficiently. By avoiding common pitfalls and leveraging tools like useMemo and UseLayoutEffect, developers can create performant and responsive React applications. Properly managing side effects ensures a smooth user experience and maintains the integrity of the application's data flow.
Are you using React in your project? If so, you must used useEffect! Actually, it’s essential for many use cases, but there are instances where it might not be the best solution, and avoiding it can improve your application's performance.
In this talk, we will learn from experience which is the missing piece of the puzzle to master useEffect. Taking a look at the incorrect cases and trying to improve their performance helps us to have a deeper understanding of it.
This talk has been presented at React Advanced 2023, check out the latest edition of this React Conference.
Using an async function directly in useEffect is not recommended because it returns a promise, which useEffect cannot handle for cleanup. Instead, you should define your async function inside the useEffect and call it there.
To avoid race conditions in useEffect, you can use an abort controller to cancel ongoing fetch requests when the component unmounts or when the dependencies change before the fetch is complete.
No, useEffect is designed to run asynchronously to avoid blocking the browser's painting of the UI. If synchronous execution is needed, useLayoutEffect should be used instead.
React uses the useEffect hook in three main scenarios: after the component mounts, when a dependency changes, and on every render if no dependencies are specified.
The useEffect hook in React allows you to perform side effects in your component, such as fetching data, setting up timers, or other JavaScript operations that should not block the rendering of the component.
When useEffect is used with an empty dependency array, it executes the callback function only once after the initial render, similar to componentDidMount in class components.
Incorrect usage of useEffect can lead to infinite loops, unnecessary re-renders, or memory leaks if dependencies are not managed correctly or cleanup functions are not used when needed.
useEffect runs asynchronously and is triggered after the browser has painted the screen, whereas useLayoutEffect runs synchronously and is executed before the screen is painted, allowing for updates to the DOM before the user sees them.
Welcome to how not to use UseEffect. UseEffect is a hook introduced in React 16.8 as a replacement for component dismount and update in class components. It runs your callback once when the component mounts and when there are changes in dependencies. UseEffect allows performing side effects such as fetching data. UseEffect executes its callback asynchronously to allow the browser to render and show something to the user without blocking the main thread. Setting a state in a useEffect without a dependency array can cause nasty loops. Sometimes you are using use effects to take care of calling parent events. Nasty Fetch. Sometimes, when fetching articles, loading and race conditions need to be considered.
Welcome to how not to use UseEffect. UseEffect is a hook introduced in React 16.8 as a replacement for component dismount and update in class components. It runs your callback once when the component mounts and when there are changes in dependencies. UseEffect allows performing side effects such as fetching data.
We grab entities from the back end, bring them to the front end, and render them accordingly. useEffect detects changes in dependencies and re-renders accordingly. It runs after the first render and again when dependencies change. On each render, useEffect is called without dependencies. It's not recommended to run side effects in the component's body.
3. Understanding the Event Loop and Promises
It's going to recall that function, recall that function, recall that function, fetch articles in this case. We want to fetch articles once. There is a react reason and UX reason behind the scene. React runs the callback connected to event loop. Event loop is a mechanism in JavaScript to handle asynchronous stuff. It works by pushing tasks into the task queue and executing them when the call stack is empty. There is also a microtask queue responsible for promises. Promises can block the main thread by continuously adding tasks to the queue.
4. Execution of useEffect Callback
UseEffect executes its callback asynchronously to allow the browser to render and show something to the user without blocking the main thread. It uses Web API, SetTimeout, and other mechanisms to grab information and present it to the user.
5. Understanding UseEffect Execution
UseEffect executes its callback asynchronously using a task queue. There is a difference between SetTimeout and ZeroTimeout, with ZeroTimeout using a message channel. React source code also utilizes the message channel. The UX reason for useEffect running asynchronously is to allow for immediate rendering and browser paint. There is a synchronous version called useLayoutEffect, which runs before useEffect. It is used when a reference to an element is needed. One situation to be aware of is the 'nasty loop', where setting a state that updates a dependency can lead to multiple network requests.
6. Understanding useEffect and Dependency Arrays
Setting a state in a useEffect without a dependency array can cause nasty loops. Objects are reference types and not equal to each other. React compares values behind the scenes. If dependencies haven't changed, it runs the callback once, similar to component did mount.
7. Understanding useEffect Dependencies and Cleanup
Somehow component did mount. The last dependency, an object containing 'label React', causes it to run on each render. The 'nasty async' case involves returning a promise instead of a function, which is not what React expects. Wrapping it with a function async solves this. Lastly, outside the render cycle, cleanup functions are necessary to revert changes made.
8. Nasty state: Filtering articles without useEffect
You can filter articles without using useEffect. Instead, use memo to achieve memoization and remove unnecessary useEffect calls.
9. Nasty event call and useEffect
Sometimes you are using use effects to take care of calling parent events. In this case, you can cut this part and just put it in HandleClick. It's pretty straightforward and easy. As soon as you set this state, open, close would be called and the React render and the browser paint. Less useEffect, more readable, and no extra React render.
10. Nasty Fetch: Loading and Race Conditions
Nasty Fetch. Sometimes, when fetching articles, loading and race conditions need to be considered. To handle race conditions, a cancellation logic can be implemented using an abort controller. This allows canceling the fetch request if the category has changed.
This transcription provides a brief guide to React rendering behavior. It explains the process of rendering, comparing new and old elements, and the importance of pure rendering without side effects. It also covers topics such as batching and double rendering, optimizing rendering and using context and Redux in React. Overall, it offers valuable insights for developers looking to understand and optimize React rendering.
Remix is a web framework built on React Router that focuses on web fundamentals, accessibility, performance, and flexibility. It delivers real HTML and SEO benefits, and allows for automatic updating of meta tags and styles. It provides features like login functionality, session management, and error handling. Remix is a server-rendered framework that can enhance sites with JavaScript but doesn't require it for basic functionality. It aims to create quality HTML-driven documents and is flexible for use with different web technologies and stacks.
The Talk discusses React Forget, a compiler built at Meta that aims to optimize client-side React development. It explores the use of memoization to improve performance and the vision of Forget to automatically determine dependencies at build time. Forget is named with an F-word pun and has the potential to optimize server builds and enable dead code elimination. The team plans to make Forget open-source and is focused on ensuring its quality before release.
Today's Talk explores the use of the useEffect hook in React development, covering topics such as fetching data, handling race conditions and cleanup, and optimizing performance. It also discusses the correct use of useEffect in React 18, the distinction between Activity Effects and Action Effects, and the potential misuse of useEffect. The Talk highlights the benefits of using useQuery or SWR for data fetching, the problems with using useEffect for initializing global singletons, and the use of state machines for handling effects. The speaker also recommends exploring the beta React docs and using tools like the stately.ai editor for visualizing state machines.
Mishko, the creator of Angular and AngularJS, discusses the challenges of website performance and JavaScript hydration. He explains the differences between client-side and server-side rendering and introduces Quik as a solution for efficient component hydration. Mishko demonstrates examples of state management and intercommunication using Quik. He highlights the performance benefits of using Quik with React and emphasizes the importance of reducing JavaScript size for better performance. Finally, he mentions the use of QUIC in both MPA and SPA applications for improved startup performance.
Routing in React 18 brings a native app-like user experience and allows applications to transition between different environments. React Router and Next.js have different approaches to routing, with React Router using component-based routing and Next.js using file system-based routing. React server components provide the primitives to address the disadvantages of multipage applications while maintaining the same user experience. Improving navigation and routing in React involves including loading UI, pre-rendering parts of the screen, and using server components for more performant experiences. Next.js and Remix are moving towards a converging solution by combining component-based routing with file system routing.
Ivan’s first attempts at performance debugging were chaotic. He would see a slow interaction, try a random optimization, see that it didn't help, and keep trying other optimizations until he found the right one (or gave up). Back then, Ivan didn’t know how to use performance devtools well. He would do a recording in Chrome DevTools or React Profiler, poke around it, try clicking random things, and then close it in frustration a few minutes later. Now, Ivan knows exactly where and what to look for. And in this workshop, Ivan will teach you that too. Here’s how this is going to work. We’ll take a slow app → debug it (using tools like Chrome DevTools, React Profiler, and why-did-you-render) → pinpoint the bottleneck → and then repeat, several times more. We won’t talk about the solutions (in 90% of the cases, it’s just the ol’ regular useMemo() or memo()). But we’ll talk about everything that comes before – and learn how to analyze any React performance problem, step by step. (Note: This workshop is best suited for engineers who are already familiar with how useMemo() and memo() work – but want to get better at using the performance tools around React. Also, we’ll be covering interaction performance, not load speed, so you won’t hear a word about Lighthouse 🤐)
In this advanced Next.js workshop, we will delve into key concepts and techniques that empower React.js developers to harness the full potential of Next.js. We will explore advanced topics and hands-on practices, equipping you with the skills needed to build high-performance web applications and make informed architectural decisions. By the end of this workshop, you will be able to:1. Understand the benefits of React Server Components and their role in building interactive, server-rendered React applications.2. Differentiate between Edge and Node.js runtime in Next.js and know when to use each based on your project's requirements.3. Explore advanced Server-Side Rendering (SSR) techniques, including streaming, parallel vs. sequential fetching, and data synchronization.4. Implement caching strategies for enhanced performance and reduced server load in Next.js applications.5. Utilize React Actions to handle complex server mutation.6. Optimize your Next.js applications for SEO, social sharing, and overall performance to improve discoverability and user engagement.
With the release of React 18 we finally get the long awaited concurrent rendering. But how is that going to affect your application? What are the benefits of concurrent rendering in React? What do you need to do to switch to concurrent rendering when you upgrade to React 18? And what if you don’t want or can’t use concurrent rendering yet?
There are some behavior changes you need to be aware of! In this workshop we will cover all of those subjects and more.
Join me with your laptop in this interactive workshop. You will see how easy it is to switch to concurrent rendering in your React application. You will learn all about concurrent rendering, SuspenseList, the startTransition API and more.
The addition of the hooks API to React was quite a major change. Before hooks most components had to be class based. Now, with hooks, these are often much simpler functional components. Hooks can be really simple to use. Almost deceptively simple. Because there are still plenty of ways you can mess up with hooks. And it often turns out there are many ways where you can improve your components a better understanding of how each React hook can be used.You will learn all about the pros and cons of the various hooks. You will learn when to use useState() versus useReducer(). We will look at using useContext() efficiently. You will see when to use useLayoutEffect() and when useEffect() is better.
Introducing FlashList: Let's build a performant React Native list all together
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In this workshop you’ll learn why we created FlashList at Shopify and how you can use it in your code today. We will show you how to take a list that is not performant in FlatList and make it performant using FlashList with minimum effort. We will use tools like Flipper, our own benchmarking code, and teach you how the FlashList API can cover more complex use cases and still keep a top-notch performance.You will know:- Quick presentation about what FlashList, why we built, etc.- Migrating from FlatList to FlashList- Teaching how to write a performant list- Utilizing the tools provided by FlashList library (mainly the useBenchmark hook)- Using the Flipper plugins (flame graph, our lists profiler, UI & JS FPS profiler, etc.)- Optimizing performance of FlashList by using more advanced props like `getType`- 5-6 sample tasks where we’ll uncover and fix issues together- Q&A with Shopify team
ReactJS is wildly popular and thus wildly supported. TypeScript is increasingly popular, and thus increasingly supported.
The two together? Not as much. Given that they both change quickly, it's hard to find accurate learning materials.
React+TypeScript, with JetBrains IDEs? That three-part combination is the topic of this series. We'll show a little about a lot. Meaning, the key steps to getting productive, in the IDE, for React projects using TypeScript. Along the way we'll show test-driven development and emphasize tips-and-tricks in the IDE.
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