Understanding how React Suspense works

Race conditions are bugs that happen due to incorrect assumptions about the order in which our code may run. Fetching data in the useEffect Hook or in class lifecycle methods like componentDidUpdate often leads to them. We’ve solved the previous network “waterfall”, but accidentally introduced a different one. We wait for all data to come back with Promise.all() inside fetchProfileData, so now we can’t render profile details until the posts have been fetched too.

The following component contains the whole of our simple example application. When throws an error, which could happen as a result of that asynchronous action, ”sees” it and switches to the error UI. I found this didnt work by assigning wrapPromise.status and wrapPromise.response as local variables because state was not retained between subsequent calls to wrapPromise.read(). This worked fine for me when I moved status and response to global scope. You can begin to see how ridiculously easy it becomes to organize your application’s loading states as opposed to having to manage isLoading variables yourself. Now that we have both components ready, let’s explore Suspense in deeper detail.

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If you’re not familiar with Error Boundaries, they are components used to wrap other components that may throw errors. Any time a child component throws an error, such as a failed network request, a wrapping Error Boundary component can toggle its rendering to show a custom error UI. Although it’s technically doable, Suspense is not currently intended as a way to start fetching data when a component renders. Rather, it lets components express that they’re “waiting” for data that is already being fetched. Building Great User Experiences with Concurrent Mode and Suspense describes why this matters and how to implement this pattern in practice. In this section, we’ve seen how React suspense can be used in multiple data fetching components.

So far, it’s the only implementation that we tested in production and are confident in. But you can use a library that’s integrated with Suspense . This https://bitcoin-mining.biz/ page describes experimental features that are not yet available in a stable release. Don’t rely on experimental builds of React in production apps.

Quick start

We can start fetching both code and data at the same time , delivering a much better user experience. Usually, the fallback is used to render fallback loading states such as a glimmers and placeholders. This is a waterfall effect, we have to wait for some code that requests the data, until it’s loaded then we can continue. To improve this, we should not wait for the response, that means we should fetching both code and data at the same time, deal with asynchronous operations, promises. If the other module fails to load , it will trigger an error. You can handle these errors to show a nice user experience and manage recovery with Error Boundaries.

We now have the “back end” for our app ready, so it’s time to build out the components. Inside this function, we initialize a new variable, promise, and set its value to a Fetch request Promise. When this request is completed, we get the data from the Response object using res.json() and then return res.data, which contains the data that we need. Notice that we’re installing the “release candidate” versions of both react and react-dom.

React Suspense

So, four repeated requests for that same “C++” search query should throw the same, identical promise. This implies some sort of caching layer to manage all this. Instead, you’ll just hope, and wait for the data library you use to update itself to support Suspense. When making Suspense boundary fallbacks, try not to throw up any sort of spinner and “loading” message.

The query will update immediately, so the input will display the new value. However, the deferredQuery will keep its previous value until the data has loaded, so SearchResults will show the stale results for a bit. Now that we have all our components ready, we’ll render them in the UserDashboard component. This component will fetch a mock todo data from the JSONPlaceholder mock endpoint, we’ll render this as a todo list on our user’s dashboard as well. Without an error boundary, our App will crash and render a blank page with errors in the console.

It lets data fetching libraries deeply integrate with React. If a data fetching library implements Suspense support, using it from React components feels very natural. For you to see the error handling within the app, you’ll need to close that overlay by clicking the “x” in the upper-right. We have a MainContent component, which is a query renderer that fetches and renders a query. MainContent will suspend rendering when it attempts to fetch the query, indicating that it isn’t ready to be rendered yet, and it will resolve when the query is fetched. In these cases, we would still show the Suspense boundary fallbacks.

Why is React Suspense useful?

Besides, using vanilla JavaScript will give us a better look at how Suspense works. We use a set of checklists to keep us on track and ensure reproducible quality on every project. That means now is the time to familiarize yourself with Suspense. While APIs might change between now and its release, general concepts will likely stay the same.

It was written by me alone, so expect parts of it to be a bit unrefined . But first, for context, I’ll briefly cover how navigation state is managed in this app, so the Suspense code will make more sense. If you’re wondering about React Router, it seems great, but I’ve never had the chance to use it. My own side project has a simple enough routing story that I always just did it by hand.

• Then, when the data loads, React hides the Loading fallback and renders the Albums component with data.
• However, this makes it more difficult to see which problems Suspense solves, why these problems are worth solving, and how Suspense is different from the existing solutions.
• Depending on the size of your application, such a pattern could be a great way to speed up the load times.
• Status is initialized to “pending” by default, because that’s the default state of any new Promise.
• The moment the URL updates, the application state governing that label is updated; however, that state does not initially display.

If you work with a designer, ask them where the loading states should be placed—it’s likely that they’ve already included them in their design wireframes. In this article, we’ve learned how React suspense and error boundary works, we also explored the React fallback UI and how to implement them in a React application or web app. The last data fetching component is a user album component that’ll fetch data from the JSONPlaceholder endpoint and render it on the user dashboard. We’ll create a suspense fallback UI for our React app, this fallback UI will be rendered before our component is fully ready to be rendered.

However, this means that we would hide existing content in favor of showing the Suspense fallback. On the client, React will attempt to render the same component again. If it errors on the client too, React will 11 Best Freelance WordPress Developers Hire in 48 Hours throw the error and display the closest error boundary. However, if it does not error on the client, React will not display the error to the user since the content was eventually displayed successfully.

Suspense essentially extends React’s reactive capabilities into the asynchronous world, allowing the developer the ability to implement a more declarative loading state for their UI. Technically, Suspense can be used anywhere in your React tree if you’re using at least React 18. That includes within client-side rendering (i.e. CSR), server-side rendering (i.e. SSR), and experimental React Server Components (i.e. RSC, since we’re giving initialisms to everything).

Error boundaries are class components in React apps that catch JavaScript errors anywhere within their child component, log the error for the developer, and render a fallback UI for the user. Notice how there’s a “C++” label to the right of the search pane, with an option to remove it from the search query? Or rather, notice how that label is only on the second two screenshots? The moment the URL updates, the application state governing that label is updated; however, that state does not initially display. Initially, the state update suspends in memory , and the prior UI continues to show. I’m grabbing the value from context, and if true, rendering an inline spinner on top of my existing results.

The re-rendered children component will no longer execute the Promise because the data is cached. React version 16.x has taken the industry by storm since its release. Among the new features in this release, the most popular are Hooks, lazy loading, Suspense, cache…etc.

However, the nested Suspense boundary around Albums is new, so the transition doesn’t wait for it. Both deferred values and transitions let you avoid showing Suspense fallback in favor of inline indicators. Transitions mark the whole update as non-urgent so they are typically used by frameworks and router libraries for navigation. Deferred values, on the other hand, are mostly useful in application code where you want to mark a part of UI as non-urgent, meaning that it’s allowed to “lag behind” the rest of the UI.

If it is a Promise, the Suspense component will recognize that the component is still waiting for some data, and it will render the fallback. If it’s an error, it bubbles the error back up to the nearest Error Boundary until it is either caught or it crashes the application. We’ll be building a simple app that fetches some data from an API and renders it to the DOM, but we’ll be making use of Suspense and the render-as-you-fetch approach. I’m assuming you are already familiar with React Hooks; otherwise, you can get a quick intro here.