Using useEffect Effectively

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Can useEffect affect your codebase negatively? From fetching data to fighting with imperative APIs, side effects are one of the biggest sources of frustration in web app development. And let’s be honest, putting everything in useEffect hooks doesn’t help much. In this talk, we'll demystify the useEffect hook and get a better understanding of when (and when not) to use it, as well as discover how declarative effects can make effect management more maintainable in even the most complex React apps.

David Khourshid
David Khourshid
30 min
21 Oct, 2022

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Video Summary and Transcription

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.

Available in Español

1. Introduction to use effect

Short description:

Hello, everyone! My name is David Corschied and I work at stately.ai. Today, we're going to talk about our favorite hook, use effect, and how it simplifies things compared to class components. Let's dive in!

All right, hello, everyone. My name is David Corschied, and my slides will be showing up shortly. I'm sure... Oh, yeah, there it is. David Corschied. I'm at David K. Piano pretty much everywhere. I'm very excited to be in London. Again, I work at stately.ai, where we think a lot about state, logic, and effects, but enough about me. If I keep going, then this talk is going to last longer than your next prime minister, so let's get on with it.

Okay. So, of course, I work at stately, and one of our engineers, Matice, you might have seen him. He's in your NPM, your node modules, I guarantee it. He's one of the most talented developers I know. Yesterday he created a PR where he asked, am I 100% confident in this fix? Hell no, it's based on use effect. So, we're going to be talking about that today, our favorite hook, use effect. But let's start from the beginning. Who remembers class components? Right? So, yeah, some people really want them back. So do I.

All right. So, in this example, I remember that when react came out, I was very excited for it. I'm like, wow, this is going to change everything, and react did change everything on every single render. So, over here, we're doing what most components do, or what most React developers do, which is fetch data and show it on the screen. Admit it. That's 90% of your job. But we had a nice, convenient, little life cycle hook component to do that in. But now things are different. We have use effect. So, I remember I learned about use effect in 2018, and I was very excited to use it because I'm like, wow, this makes things a lot simpler. So instead of making these big, bulky classes, we have these hooks that we can put things in.

2. Fetching Data with Use Effect

Short description:

I wanted to fetch data using new JS syntax in 2018. However, when I put it in use effect, React yelled at me. It didn't know what to do with the async await syntax, so I had to use .then instead. Even though I thought I had it figured out, the next day my AWS failed due to an infinite loop caused by continuous fetching. I realized I needed to read the documentation and discovered the tip about using a dependency array. By adding an empty array, I could optimize performance and avoid infinite loops.

I wanted to fetch data. It was 2018, so I wanted to use new JS syntax. And it was in effect. So, I put it in use effect.

Tried this, React yelled at me. It said, listen, this async await stuff, it's fancy, but you cannot use it like that. You have to, you know, we, it doesn't infer that, hey, I don't know what to do with this because it promises that you return from use effect. So, we had to do things like it was 2015 and use.then.

So, I fetched some data, then I set the data. I'm like, this is simple. I just put it in the use effect. I get my data. I'm good to go. Right? Wrong. Guess what happened to my AWS fail the next day? Yeah. So, this, by the way, it will keep fetching and fetching and fetching. And it really won't, React won't tell you that, hey, this is going to occur as an infinite loop.

All right. So, at this point, I'm like, okay, maybe I should read the documentation a little bit. So, I scrolled all the way down. And so, there was a tip. It's just a tip. You know, this very crucial bit of information is a tip in the current React docs. Docs optimizing performance by skipping effects. And so, I learned that you're supposed to use this little dependency array. And since this didn't really have any dependencies, you just put it empty like that. If you look at it sideways, it sort of looks like an agonized React developer screaming into the void.

So... Yeah. All right.

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