Understanding the purpose and functionality of UseEffect.
Recognizing the importance of dependency arrays in UseEffect.
Avoiding common mistakes like infinite loops and improper async usage in UseEffect.
Implementing cleanup functions to manage resource cleanup effectively.
Exploring alternatives like useMemo for optimizing performance.
The UseEffect hook in React is an essential tool for managing side effects in functional components. Its introduction in React 16.8 marked a significant shift from class components, providing a simpler and more efficient way to handle component lifecycle events. UseEffect allows developers to perform actions such as data fetching, subscriptions, or manual DOM updates after a component renders.
At its core, UseEffect takes two arguments: a callback function and a dependency array. The callback function contains the side-effect logic, while the dependency array determines when the effect should re-run. Properly using this dependency array is crucial to avoid unnecessary re-renders or infinite loops.
The most straightforward use case for UseEffect is executing a callback once when a component mounts. By passing an empty array as the second argument, the effect runs only once, making it ideal for initial data fetching. For example, fetching articles from an API when a component first loads can be efficiently handled with this pattern.
Another common scenario involves triggering the effect when specific dependencies change. By listing these dependencies in the array, UseEffect will re-run the callback whenever any of them change. For instance, if fetching articles based on a category ID, including that ID in the dependency array ensures the data is updated accordingly when the category changes.
It's important to note that UseEffect runs after every render by default if no dependency array is provided. This behavior can be problematic, especially when dealing with state updates or side effects that don't need to run on every render. Developers should be cautious and deliberate when deciding which dependencies to include.
A common pitfall with UseEffect is creating infinite loops. This can occur if a state update inside the effect causes a re-render, which then triggers the effect again. To avoid this, ensure that state updates within UseEffect do not inadvertently affect its dependencies, or use conditions to control when updates occur.
Using async functions directly inside UseEffect can also lead to unexpected behavior. Since async functions return promises, they are not directly compatible with the cleanup function UseEffect expects. To handle asynchronous logic, it's better to define an async function within the effect and call it, allowing for proper handling of promises and cleanup.
Cleanup functions are vital in UseEffect to prevent memory leaks and ensure resources are released appropriately. For example, when setting up event listeners or intervals, including a cleanup function to remove them when the component unmounts is crucial for maintaining performance and preventing unwanted behavior.
Alternatives like useMemo can sometimes replace UseEffect when dealing with expensive calculations or derived state. useMemo helps optimize performance by memoizing the result until dependencies change, reducing the need for unnecessary re-renders.
Another consideration when using UseEffect is managing asynchronous operations with race conditions. Implementing logic to cancel pending requests or using tools like AbortController can prevent unwanted updates when a component's state changes quickly.
Sometimes, developers use UseEffect to call parent component functions or manage state updates. In such cases, consider whether the logic can be integrated directly into event handlers to simplify the component structure and avoid additional renders.
Effectively using UseEffect requires understanding its purpose, managing dependencies carefully, and implementing cleanup functions. By avoiding common pitfalls and exploring alternatives like useMemo, developers can harness the full potential of UseEffect to create efficient and maintainable React applications.
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.
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.
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.
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.
2. Understanding useEffect and Dependencies
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 🤐)
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.
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.
In this workshop, you'll learn how to build your first full stack dapp on the Ethereum blockchain, reading and writing data to the network, and connecting a front end application to the contract you've deployed. By the end of the workshop, you'll understand how to set up a full stack development environment, run a local node, and interact with any smart contract using React, HardHat, and Ethers.js.
React Testing Library is a great framework for React component tests because there are a lot of questions it answers for you, so you don’t need to worry about those questions. But that doesn’t mean testing is easy. There are still a lot of questions you have to figure out for yourself: How many component tests should you write vs end-to-end tests or lower-level unit tests? How can you test a certain line of code that is tricky to test? And what in the world are you supposed to do about that persistent act() warning? In this three-hour workshop we’ll introduce React Testing Library along with a mental model for how to think about designing your component tests. This mental model will help you see how to test each bit of logic, whether or not to mock dependencies, and will help improve the design of your components. You’ll walk away with the tools, techniques, and principles you need to implement low-cost, high-value component tests. Table of contents- The different kinds of React application tests, and where component tests fit in- A mental model for thinking about the inputs and outputs of the components you test- Options for selecting DOM elements to verify and interact with them- The value of mocks and why they shouldn’t be avoided- The challenges with asynchrony in RTL tests and how to handle them Prerequisites- Familiarity with building applications with React- Basic experience writing automated tests with Jest or another unit testing framework- You do not need any experience with React Testing Library- Machine setup: Node LTS, Yarn
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