React get async data before render
Dec 19, Now and then I face issues and try to find answers, but this one I havn't found a proper way to do it. Being from angular background I'm facing tough time to handle null conditions on object, because without props getting updated with appropriate data object might throw errors.
Ricardo Memoria. In order to make the exemple as simple as possible, I'm using the component internal state to control if the asynchronous call has already returned or not. Like that:. The trick here is to use the component internal setState. Every time you call setState, React will force the component to render again. So, suppose you have an asynchronous function getSomeData that will call a callback function when data is fetched from server.
When this function is called, I set the state of the component with the data and the render function is called again. Inside render, I use an AND operation to check if the data property is available in state.
Since state is not initialized by default, I have to test if state and state. This is a very simple technic, but it works pretty well When you get deeper into React, you'll find a lot of best practice guides recommending to avoid the use of internal component state for example, stripping out the async call from inside the component and passing the data as a component propertywhich offers some advantages in terms of maintainability.
But that is another history Godti Vinod. Jul 26, GuardMe Company. Jun I don't know if this answer is going to get to you and you could answer it but I have a problem similar to that one. My structure consists on:. When I make the call to get the messages of a chat, this call is asynchronous, so the setState must be done afer it has finished as you mention.How to use Async Await in React?
But if you work with your own webpack boilerplate you may hit regeneratorRuntime is not defined.
Update on Async Rendering
Before starting off make sure to have a React development environment. To make one you can follow this tutorial of mine: How to set up React, webpack, and babel or you can also use create-react-app.
Let's say you want to fetch data from an API. This component is a contrived example: there's no error handling. NOTE : you can write the very same component as a function with the useEffect hook. Nothing fancy right? Can we do better?
Let's try! Supported since version 7. On the front-end it's another story. I know, who cares about IE? But if you have a webpack boilerplate you may hit an error more in a minute. Open up App. No error catching, again, let's assume nothing goes wrong with our fetch call. Take a look at the browser's console: regeneratorRuntime is not defined?
What's that? The key for fixing that error are babel preset env and babel plugin transform runtime. Make sure to install them:. Save the file run the build again if you don't have webpack-dev-server and check out the browser. It should work! But we're not done yet. How about errors? What happens if the user goes offline or the API goes down?
The example we saw so far doesn't handle errors. Granted, in real world apps you would decouple fetch calls from the view.
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Moreover, the Fetch API has some caveats when it comes to handling errors. There is an uncaught error of course.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign in to your account. It would seriously ease the process of building something isomorphic if componentWillMount could return a promise and that react would delay rendering until that promise is resolved.
I have seen attempt of doing something like that in react-router and rrouter, however giving this responsibility to each component instead of a router module would make more sense for me. The main reason I believe that this doesn't exist already is that on the client side, you basically always want to show some sort of loading indicator instead of deferring rendering. It would also make the code significantly more complex, but we can probably deal with that. That do the trick but in my point of view those are just hackish solutions to solve a problem that can only be solved in core.
Color me uninformed on this subject, fdecampredon say that componentWillMount is async and you don't return anything immediately, what is React supposed to render until there is, nothing? If so, why not just return nothing in render if there is no data yet?
Yeah I get server-side Also, what should happen if props change before componentWillMount fires? Personally, it seems like it's wrong to dispatch async requests during componentWillMount unless the component really is an isolated black box and also implements a loading indicator.
As far as I understand it, React components should not be mistaken for more conventional OOP instances. In the best case, a React component is tool for visualizing the data in props, if it's interactive then possibly also state. It's a view, not a view and model.
To my ears, that sounds like the problem, React components shouldn't be the ones dispatching the async requests, you fetch all the data and when that data is ready, only then do you call React.
Same solution client-side and server-side. You also get the ability to abort with an outcome of your choice if any async request fail.
Feel free to dismiss me if I misunderstood something, but it seems that you're treating React components as view and model, when it seems they're meant as just the view. This feature would be useful only the first time we mount the top level component, and on the server, it's true that otherwise In most cast you would want to display a loader indicator.
In a way or in other you'll want that a 'top-level' component would be able to retrieve data, like it's done in the Flux sample. In this sample things are pretty simple because retrieving the list of todo is a synchronous operation, if it was not, and in case of pre-rendering on the server, we would render a first time with no data and loose the pre-rendered markup from server. In the case of a simple application with one set of data displayed by one view hierarchy there is still not so much problem, you can preload data and still keep the synchronous property of your store.
Now in case of an application composed of multiple modules that you reuse across your application I would like to be able to treat those modules as separate applications that are able to 'subscribe' on different stores that would be responsible for fetching data. But I'm guessing the devs at Facebook must've run into this themselves a few times.
Any update on this? I've just started exploring React and I immediately run into this. Many people recommend React as a go to solution for building isomorphic apps, but as long as this is not solved I think it simply can't get the job done. And that would be a shame because there is such a potential. I really understand fdecampredon when he mentions those complex applications composed of multiple modules.
React would be perfect for this. I don't think that this approach would mean treating a component as view and model. If you look at the Flux architecture, they think of React components as of controller-views that not only display data from stores but also invoke actions based on user interactions.
To me it sounds just like an obvious MVC architecture.September 11, 6 min read It aims to help with handling async operations respectively in regard to CPU power and data fetching.
Suspense allows you to defer rendering part of your application tree until some condition is met for example, data from an endpoint or a resource is loaded. This is a common method used to ensure good UX for apps that are fetching data from external sources. All you have to do is check if the data has been successfully fetched, and if not, show a spinner. The key module that makes Suspense work is the createFetcher function. Available on npm as the simple-cache-providerit works as outlined below:.
We create a fetcher function using createResource from the simple-cache-provider package. Note: The simple-cache-provider is still an experimental feature, not to be used in a production app.
When initiating createResourcea function is passed which is expected to return a Promise. If the Promise resolves, React carries on and render the results, else, an error is thrown. The codebase for the demo can be accessed on GitHub and the live demo can be accessed here. Run the command below in your terminal to generate a React app:. This creates a folder titled react-suspense which contains the React app.
Therefore, your package. The alpha version shown above is the version of React we need to carry out our tests.
Run the npm install command to update all dependencies. The first will be to import the createResource function in the App. Create a folder, name it components and in it create a. Consumer and puts the cache over the wrapped component. In the App. In the code above, a stateless component is created and wrapped in the withCache Higher Order Component.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have a component, which relies on data to be asynchronously retrieved before the content is rendered.
If the data is not yet available, the render function will return a Loader component instead:. This works ok, but what if I wanted to add in another async fetch call in parallel? How would I properly wait for both to finish before setting the state of 'loading' to false?
Using Promise. You have more than one option here I think but if you already use redux why don't you move your logic there?
With the help of redux-thunk you can do your asynchronous operations in your action creators and use a global process state. This is an example of async functions but you can use promises of course. When you want to make multiple async operations just fire your action creators and they increment the process by one. In your component, you will check if your progress state is greater than 0 or like if progress shortly than show a loading component. Learn more. Wait for multiple async calls to finish before React render Ask Question.
Asked 1 year, 7 months ago. Active 1 year, 7 months ago. Viewed 7k times. If the data is not yet available, the render function will return a Loader component instead: if this. Rolodecks Rolodecks 1 1 gold badge 3 3 silver badges 10 10 bronze badges. Some where in your react data store, you will need to set the loading flag to true.
I am assuming that you are using flux or redux model.REACT JS TUTORIAL #4 - State vs Props & Application Data
If you set the flag to true, then the data store will go through return the flag.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.
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Sign in to your account. I couldn't find this mentioned in the RFC. Currently almost all of our components implement compoentWillReceiveProps to trigger some async operation in reaction to props changes, then call setState asynchronously.
Simple example:. Note that the above example is very simple, is prone to race conditions if the responses arrive out of order and does no cancellation on new values or component unmount. So now that the methods we were making use of are deprecated, I wonder were we doing this wrong all the time?
Is there already a better way to do this with the old API? And what is the recommended way to do this with the new API? I think the RFC is pretty clear about this. I'm currently in the process of writing some blog posts to go over this, but I'll answer here with similar content in case it's helpful for others who come across this issue in the future. I think it would be helpful to start with a quick overview of how React works, and how async rendering will impact class components.
The commit phase is usually very fast, but rendering can be slow. For this reason, async mode will break the rendering work into pieces, pausing and resuming the work to avoid blocking the browser. This means that React may invoke render phase lifecycles more than once before committing, or it may invoke them without committing at all because of an error or a higher priority interruption. Because the above methods might be called more than once, it's important that they do not contain side-effects.
Ignoring this rule can lead to a variety of problems. For example, the code snippet you showed above might fetch external data unnecessarily. For these reasons, we suggest moving it to componentDidMount. There is a common misconception that fetching in componentWillMount lets you avoid the first empty rendering state.
In practice this was never true because React has always executed render immediately after componentWillMount. If the data is not available by the time componentWillMount fires, the first render will still show a loading state regardless of where you initiate the fetch. This is why moving the fetch to componentDidMount has no perceptible effect in the vast majority of cases. Just in case it's unclear, the old lifecycle, componentWillReceivePropswas also synchronous.
This means that you'd still have a render in between when the new props were set and when external data finished loading. So the suggested pattern above won't require any additional renders.
Using componentWillReceiveProps exacerbates this problem, for reasons explained above. Hopefully you're using a library like Axios or managing cancellation in some other way. Legacy lifecycles like componentWillReceiveProps will continue to work until React version Our preference is that people will migrate to using the new lifecycles though!
I was using a similar pattern in lots of my components for ajax requests.This page describes experimental features that are not yet available in a stable release. These features may change significantly and without a warning before they become a part of React. This documentation is aimed at early adopters and people who are curious. React This page focuses on the data fetching use case, but it can also wait for images, scripts, or other asynchronous work.
In this exampletwo components wait for an asynchronous API call to fetch some data:. Try it on CodeSandbox. This demo is a teaser. Suspense is not a data fetching library. React can then wait for it to be ready and update the UI. At Facebook, we use Relay and its new Suspense integration.
We expect that other libraries like Apollo can provide similar integrations. In the long term, we intend Suspense to become the primary way to read asynchronous data from components — no matter where that data is coming from. Suspense is significantly different from existing approaches to these problems, so reading about it for the first time often leads to misconceptions.
At Facebook, so far we have only used the Relay integration with Suspense in production. It demonstrates patterns that have already worked well for us in production. This page is more conceptual and is intended to help you see why Suspense works in a certain way, and which problems it solves. Over the next several months, many libraries will appear with different takes on Suspense APIs. If you prefer to learn when things are more stable, you might prefer to ignore this work for now, and come back when the Suspense ecosystem is more mature.
We expect to see a lot of experimentation in the community with other libraries. There is one important thing to note for data fetching library authors.
Building Great User Experiences with Concurrent Mode and Suspense describes why this matters and how to implement this pattern in practice. Unless you have a solution that helps prevent waterfalls, we suggest to prefer APIs that favor or enforce fetching before render. Suspense for Data Fetching is still experimental, so you can expect our recommendations to change over time as we learn more from production usage and understand the problem space better.
We could introduce Suspense without mentioning the popular data fetching approaches. 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.
This is a bit simplified, and in practice solutions tend to use a mix of different approaches. Still, we will look at them in isolation to better contrast their tradeoffs.
Waterfalls are common in code that fetches data on render. Libraries can prevent waterfalls by offering a more centralized way to do data fetching. For example, Relay solves this problem by moving the information about the data a component needs to statically analyzable fragmentswhich later get composed into a single query. We wait for all data to come back with Promise.
We have to wait for both. Of course, this is possible to fix in this particular example. We could remove the Promise. However, this approach gets progressively more difficult as the complexity of our data and component tree grows. So fetching all data for the new screen and then rendering is often a more practical option. In the previous approach, we fetched data before we called setState :.
In fact, we start rendering pretty much immediately after kicking off the network request:.