React fetch data undefined

To fetch API data in function components, we use useState and useEffect hooks. SWR. Let’s look at various examples using components, hooks and helpers to see how we can implement loading states when making requests. The Setup Before we start getting fully into the Apollo Client, let’s start by creating a React project, or you can use the next base React project since the code One possible solution is to give your variable a default initial value, with useState it would look like that: const [items, setItems] = useState([]); This means that when react runs our useState ( []) call, it will return us with. We encase the method call with a try…catch block so that we can capture any errors. To learn how to fetch data from the server and use it to update the contents of a web page. Mar 19, 2020 · This is the full component. This guide will demonstrate how to correctly fetch data from a JSON file in your React app and consume it on the frontend. Fetching data from a data source is considered as a basic requirement of any mobile application. With functional components, the counterpart is useEffect. Jul 04, 2021 · During initial rendering React still determines what is the output of the component, so there’s no DOM structure created yet. A similar issue we can find in React JS. This is also a good spot to do data fetch calls. Sometimes we are required to interact with APIs that are being called in rapid succession from our web app. Aug 23, 2020 · There are many times where we want to fetch a bunch of data when the component is mounted in React. I found 2 ways to do that. import React, { Component } from 'react' import '. prefetchQuery. Handy for working with asynchronous function calls: these tools make it easy to use data in components without knowing when it will become available and help eliminate the undefined issue you were Answer: This question lacks a lot of context. 'map' is the property the code was trying to read; This one is another great clue. Jun 05, 2020 · Data fetching is a core requirement of almost every real-world React app. It is a common practice to fetch the data from SharePoint site, Office 365, MS Graph API, or from any external service and display it in SharePoint framework web part. The fetchUsers function is used to initiate the fetch and pass the promise to wrapPromise. So you have to put some check and access that key only when it is available. The query arg is used as a cache key. Aug 07, 2017 · If you’ve used fetch to retrieve data from an API using Javascript, doing it with React will be pretty similar. Since the fetch API is included in all modern browsers, you do not need to install a third-party library – you only need to install react-query within your application. Feb 18, 2021 · The Fetch API is the default tool to make network in web applications. It’s already possible to do that using the `componentDidMount()` lifecycle method, but with the introduction of Hooks, you can build a custom hook which will fetch and cache the data for you. User authenticated can use the web app (ex: see a list of products) the Aug 03, 2018 · The Fetch API provides an interface for fetching resources. The most voted answer which suggests to do in componentWillMount (), a method fired off before render () in React lifecycle will be completely deprecated in React v17 (as of current writing on 5/10/2020 React is Jun 20, 2020 · The last successfully resolved data for the query. You’ll notice a “loading” message when this happens. Contribute to MrCheater/react-fetch-data development by creating an account on GitHub. That’s what this tutorial will 2 days ago · My userData return undefined react js fetch. If you would like to explore more exciting stuff about React, take a look at the following articles: Top 4 React form validation libraries, React useReducer hook – Tutorial and Examples, React: “I agree to terms” checkbox example, Most popular React Component UI Libraries these days. Here we have a simple component. To use the async/await syntax, we need to wrap the axios. Instead, a feature called Suspense will be in charge for it. Other data structures need to be encoded beforehand as one of the above types. useState is analogous to class components’ state and setState. It’s generally a good idea to cancel your Ajax requests if you no longer actually care about the response, but it’s only recently become possible with fetch thanks to AbortController. [[], fn] Which means that in the first render of our component, react will “see” our items as an empty array 2 days ago · My userData return undefined react js fetch. Nov 10, 2020 · Data fetching (when you retrieve data) is usually reactive in a React applications, meaning that a prop will change, a component will render and an associated side effect of fetching new data should be triggered. We want to fetch data at our App component. That is one level above your src folder, the same place where you have your package. Thank you for reading, and have a good one! Feb 15, 2021 · We’ve walked through an end-to-end example of fetching data with hooks and Axios. current evaluates to undefined during initial rendering. Before we get to React cache control—in particular, caching content with Hooks—let’s first see how we do simple data fetching in function components. The main problem is the fetch is not getting the data from the JSON file. Feb 07, 2021 · A very common need, when you use React Router with dynamic parameter, is to fetch the data we need to show in the page. Mutations, like saving a form are typically imperative. [[], fn] Which means that in the first render of our component, react will “see” our items as an empty array Introduction. Oct 23, 2019 · Sooner or later you will need to fetch data from an API, let's have a look at how we can handle data in React!👌. useFetch. The variable “response” that receives the http data had to use await to May 03, 2021 · 5. The wrapPromise function returns an object with a read () method which behaves in the manner React Suspense expects. Jun 19, 2021 · This post will quickly go over how to make use of the useEffect hook in React to retrieve data from an API. isLoading One possible solution is to give your variable a default initial value, with useState it would look like that: const [items, setItems] = useState([]); This means that when react runs our useState ( []) call, it will return us with. If you are familiar with class components in React, you know that we can use componentdidmount. If using tree data, goes through all the nodes for the data you provided, including nodes that have children, but excluding groups the grid created where gaps were missing in the hierarc ก่อนหน้านี้ทีม facebook/react ได้เคยสร้าง library ที่ช่วยให้การ fetching data ทำงานร่วมกับ React Suspense ได้ แต่ตอนผมเริ่มค้นคว้าเรื่องนี้ก็ดันหา Doc ไม่ 2 days ago · My userData return undefined react js fetch. However there is always a confusion on which React method is the best place to fetch the data. User authenticated can use the web app (ex: see a list of products) the Feb 12, 2021 · 1. One is to declare the route in this way: <Route path="/project/:id"> <SingleProject /> </Route> Notice the /project/:id path. Let’s create our own custom hook called useFetch which helps us to fetch the data from the API. json but Data undefined when using Fetch API. useEffect(callback, []) hook invokes the callback right after mounting, when the input element has already been created in DOM. May 26, 2021 · Another way to get or fetch data from the server using the async/await function. Manually place the data into the cache using queryClient. js but feel free to use Create React App too or other web application bundler. We Nov 30, 2018 · ReactJS is commonly used to develop solutions in SharePoint Framework. I wrote this tutorial with Typescript but just a few things are typed so with minimal changes you can use it as it is in Javascript as well. When a user first logs in or accesses the app, there’s a certain amount of data React componentDidMount() is a hook that gets run once or multiple times when a React component has mounted. /components Dec 14, 2019 · Then, we want to fetch our data by using the fetch API. If these instances are not carefully planned, we could easily end up degrading the performance of the app as well as the API. Here’s the thing: React does not wait to render. So first thing first, we have to import Axios. As you can see, we have successfully fetched the data from API and shown in console. css'; import Home from '. json but Aug 22, 2021 · React-query series Part 3: Data fetching with the useQuery hook. setQueryData. As of now the following code prints the data in console but i need the same kind of output over the webpage. useEffect is a React Hook that accepts a callback as it’s the first argument. Hi All, Iam also getting similar issue TypeError: Cannot read property 'map' of undefined react, when I want to destructure an item array return items. Let's have a look at the bigger picture first and then dig deeper. log Aug 03, 2018 · The Fetch API provides an interface for fetching resources. () Here is a React Hook which aims to retrieve data on an API using the native Fetch API. env file and your variables returned undefined check the below items. First, the big one: componentWillMount is deprecated as of React 16. Store the default data as state, e. Many people tend to get confused, how to integrate their back-end code ( Node-express, Python-flask etc). Apr 28, 2020 · So, we have a basic implementation of how we can fetch data in functional React components using hooks: useState and useEffect. The data is frequently updated, which requires request-time data fetching. Because a dashboard is a private, user-specific page, SEO is not relevant and the page doesn’t need to be pre-rendered. SWR works with three main steps: first, it returns the data from the cache (the stale part), then sends the fetch request (the revalidate part), and finally comes with the up-to-date data. This hook returns the core query object, and it will detect the usage of it, and suspend (if enabled) when the data is being fetched for the first time, and update the component when any of the requested data changes. If you don’t know about react hooks then check out previous tutorial. json()) }) // the JS enginw won't wait the previous fetch to resolve, but will evaluate this statement // and the data is still not came back so it's undefined console. May 18, 2021 · Fetching Data From an API With the Fetch API in React. setState() This will cause an automatic rerender after the data is fetched. In this post, you’ll find the common scenarios of how to use fetch() with async/await syntax. A working React playground. Nov 30, 2020 · JavaScript. Oct 07, 2020 · As fetching data from an external source is still an asynchronous task, there are a number of errors you can run into while loading data from a JSON file. It also provides a global fetch () method that provides an easy, logical way to fetch resources asynchronously across the network. Where in the component lifecycle should I make an AJAX call? You should populate data with AJAX calls in the componentDidMount lifecycle method. Active today. Using the API, you will get ten users and display them on the page using Vanilla JavaScript. This Some popular ones are Axios, jQuery AJAX, and the browser built-in window. So it has no opinion on how to request remote data. May 28, 2021 · In a React Query application, when a page loads the first time, the library will fetch the data from the API, present it to you and then cache it. Add the following JSX code below the <header> tag (you can comment out, or delete, the <pre> block that we just added). add the following code to your JavaScript file. fetch. then(function(response) { // here the promise is resolved so you can see the data // so if you want to perform some changes here's the place console. We’ll use Axios to retrieve our data rather than the standard fetch api that comes with Javascript. Dec 04, 2020 · There is a variety of ways to fetch data in React, including using the built-in Fetch API, Axios, async/await, and more. Features# Composability Data undefined when using Fetch API. Apr 20, 2021 · Display API Data with React Hooks. I used Parcel. Fetching data from an API, communicating with a database, and sending logs to a logging service are all considered side-effects, as it's possible to have a different output for the same input. js, reactjs. When fetching based on a new query key, the value will resolve to the last known successful value, regardless of query key; latestData: Any. Fortunately, we can see the response data and can use dot-notation to extract the data that we need. A vet who codes. May 10, 2020 · When you quickly google 'fetching data before first rendering in React', this is the first answer that popped up from StackOverlflow. From what I can tell it is passing correctly to the component (what I thought was the problem initially). of undefined is a clue about the value of the variable Oct 30, 2019 · Fetching and rendering data from a server is very common in a React application. Synchronous action creators; Asynchronous action creators; Getting started. This looks like the logical place to fetch data. Jul 13, 2020 · There is a high possibility that a lot of components in your React application will have to make calls to an API to retrieve data that will be displayed to your users. Jun 21, 2019 · Data fetching, setting up a subscription, and manually changing the DOM in React components are all examples of side-effects. This page focuses on the data fetching use case, but it can also wait for images, scripts, or other asynchronous work. # react # javascript # webdev # hooks. g empty array / empty object. Fetch Data from an API Learn the basics of asynchronous functions and promises by fetching data from an API using fetch, useEffect and useState React Hooks Handbook Aug 21, 2020 · For this example our app will be made with Typescript and React. Jul 20, 2021 · Approach: First make the necessary JavaScript file, HTML file and CSS file. This effectively goes through all the data that you provided to the grid before the grid performed any grouping. hooks, javascript, react. Ask Question Asked today. Ever. The team behind Next. You can also fetch data in higher-order components and render props, from a GraphQL backend, and more. For us Axios gonna take care of that. json The Jun 26, 2020 · Even if there are alternatives to mocking fetch requests in tests Stop mocking fetch, this approach can be useful in complex situations when setting up an asynchronous unit test would be tricky. The corresponding data property on the query is the data received from the successful fetch or if the query's enabled property is set to false and has not been fetched yet data is the first initialData supplied to the query on initialization. Apr 30, 2019 · Click on the arrow head as given below. Fetching data using React Query is quite simple. Dec 08, 2020 · In this article, we’re going to go through some examples of how to fetch and display data from a GraphQL API in a React project using the Apollo Client state-management library. We are using the create-react-app command line tool to generate the new react app boilerplate. Feb 22, 2018 · Aborting Fetch Requests in React. json but How to fetch data in React, Fetching data with React Hooks. What is the problem here? Originally page loading on the web was simple — you'd send a request for a website to a server, and as long as nothing went wrong, the assets that made the web page would be downloaded and displayed on your computer. js has created a React hook for data fetching called SWR. Jan 27, 2020 · Simple GET request using fetch. json but Feb 12, 2021 · 1. . Fetch it just before the component will mount, right? There are a couple problems though. If you set the variable in . Suspense for Data Fetching is a new feature that lets you also use <Suspense> to declaratively “wait” for anything else, including data. Let’s take this example code. We will use the fetch function to get the data from the API. Connect: Extracting Data with. SWR is a React Hooks library for data fetching. All you need to do is define a fetch function and then pass it as a parameter to the useQuery mutation. env files. It’s a React Hooks library for remote data fetching. Step by step implementation to fetch data from an api in react. Define a constant data and store the data in JSON form by Feb 01, 2021 · The issue Cannot read the property of undefined is quite common in JavaScript. It is simple enough yet quite Dec 20, 2019 · React hooks are JavaScript functions which help us to use react features in functional components. npm install enzyme enzyme - adapter - react - 16 sinon -- save - dev Once you have your test setup, you can write your first test suite for the data request in React scenario. React fetch data in server before render. The library Note: In the future, React Hooks are not be intended for data fetching in React. 2 days ago · My userData return undefined react js fetch. useFetch custom react hook. The patterns we will cover Dec 14, 2019 · Then, we want to fetch our data by using the fetch API. json but Fetching data with React# useQuery# React hook that uses the main design of GQty. I am trying to get the json data using fetch() method and display it over a webpage using reactjs. Mar 09, 2020 · In this tutorial, we will learn about how to fetch data from the API in redux by using the redux-thunk middleware. So far, data fetching required a class-based component with state and lifecycle methods. We’ll use it to fetch data from a third-party API and see how to use it when fetching data from an API built in-house. Jul 06, 2020 · Posted by Cory House July 6, 2020 July 15, 2020 3 Comments on Four Ways to Fetch Data in React React is a focused component library. But no worries, SWR handles all these steps for us. When you fetch data asynchronously, the component will render at least once before that data is loaded – regardless of whether it’s fetched in the constructor, componentWillMount, or componentDidMount. Like I said, there are a lot of ways to do this :) Working Code Example. Data Fetching with React Hooks Sep 13, 2020 · Photo by Damir Spanic on Unsplash What We Will Learn. There are many ways to supply initial data for a query to the cache before you need it: Declaratively: Provide initialData to a query to prepopulate its cache if empty. log (response. 6, even before hooks! All the other fancy things, like SuspenseList, useTransition, useDeferredValue, priority-based rendering etc are not officially out. About How to start JavaScript Work with me Recommended tools Blog 2 days ago · My userData return undefined react js fetch. On terminal run 'yarn add Axios', it will install Axios on our project. 3 (March 2018). Leaving the dependency to be undefined (not passing the second argument to the useEffect) will make the method inside run every How to fetch data in React using Axios HTTP client Axios is another popular option which you can use to make HTTP requests in React Component. get () function call within an async function. Changing the query arg will tell the hook to re-fetch the data if it does not exist in the cache already. so I have posts on React, TypeScript, SASS & Electron. This sends an HTTP GET request from React to the npm api to search for all react packages using the query q=react, then assigns the total returned in the response to the component state property totalReactPackages so it can be displayed in the render() method. As the first argument passed in to connect, mapStateToProps is used for selecting the part of the data from the store that the connected component needs. To solve this best way is to create a URL on server which takes data as json from server and process it and reply with json data, using a post request. This is a screenshot of the UI: Fetching and Displaying the REST API. You can see an example of Jun 15, 2018 · fetch(URL) . Similar to forEachNode, except lists all the leaf nodes. /components/home' import Contact from '. A React hook that automatically triggers fetches of data from an endpoint, and 'subscribes' the component to the cached data. mapStateToProps. This post assumes that you have a general understanding of how to fetch/retrieve data from an API as well as the fundamentals of React and React Hooks. We analyze the issue and try to find a solution. While fetch() is generally easy to use, there some nuances to be aware of. map(item => 2 days ago · My userData return undefined react js fetch. Try to do your data fetching in componentDidMount() Use state and this. Now, you have obtained the knowledge to Fetch data from API in React Native. js file and add a state object to hold our todos once we Jun 22, 2020 · SWR is an initialism of stale-while-revalidate. Using Fetch. As we said earlier we are going to use the browser fetch API to consume JSON data from the todos API endpoint. In this post, I’ll walk you through the steps to use fetch to get data from an API using React, but I’ll be going slow enough that, even if this is your first time using an API, or you’re fairly new to react, you’ll Jul 31, 2019 · React Async is a promised-based library that makes it possible for you to fetch data in your React application. Imperatively: Prefetch the data using queryClient. The data that we want to display will be held within an array where we’ll want to access various elements within it. In order to retrieve data from a given URL, it provides fetch API, fetch API is a networking API which works in a similar way like a rest API, fetch API accepts URL of the source as an argument from which data needs to be fetched. You can use any HTTP client you want, but here, I just want to make things simple. log 2 days ago · My userData return undefined react js fetch. A derived boolean from the status variable above, provided for convenience. SWR first returns the data from cache (stale), then sends the request (revalidate), and finally comes with the up-to-date data again. May 12, 2021 · Posted By: Anonymous. We are making an HTTP get request to the Json Placeholder api using fetch method once the json data receives from the API, we are adding that data into the div element we just created. Defaults to undefined. Try something like: Sep 13, 2020 · Photo by Damir Spanic on Unsplash What We Will Learn. Sep 13, 2020 · Photo by Damir Spanic on Unsplash What We Will Learn. When you visit this page a second time, React Query will first return data from the cache and then perform a fetch in the background. Meaning it should be like setState (state => {}) and not “setState (newState)`. For example we have a list of projects, and clicking it goes in the project detail with the URL /project/PROJECT_ID. Keep reading to learn how. Apr 01, 2021 · It didn’t get that far, because items is undefined. You’ll understand how to fetch data, handle fetch errors, cancel a fetch request, and more. API Data Fetching in Function Components. Inside the first argument, we perform all the effect-related tasks. Fetch Data from an API Learn the basics of asynchronous functions and promises by fetching data from an API using fetch, useEffect and useState React Hooks Handbook Here is the simplest way to start working with a GraphQL API from your React app using the Fetch API. No external libraries needed!» Join the React Bootcamp→ Because a dashboard is a private, user-specific page, SEO is not relevant and the page doesn’t need to be pre-rendered. Axios is Promise-based and works for both client (Browser) and server (Node) so you don't need to worry about, whether you hit a request from the server or in your browser. How to use async/await with forEach ( oneliner ) GIT: Learn by doing. First, in the src/App. Check out this CodeSandbox to see a working version of this app. Now we just have to show these data in the app. json but How to fetch data in React using Axios HTTP client Axios is another popular option which you can use to make HTTP requests in React Component. For this example, we're going to use JSONPlaceholder, an fake REST API that allows us to test our front-end applications. The application we’ll be building is a simple JavaScript Jargon app that’s based on the Simplified JavaScript Jargon available from this Introduction. To get the news (data) from multiple website will be same, as you do with single website, fetch the data in RSS format, convert it into JSON and use the above code snippet 🤟🏻. It will probably eventually be an array, but due to the asynchronous nature of React, you are experiencing at least one render when the variable is undefined. While Axios will ultimately be used to fetch external data Soon (or maybe even now) you’ll be able to use React’s built-in Suspense feature to fetch and cache data. This comment has been minimized. This kind of functionality was previously achieved using Apr 05, 2020 · Getting Data from API. We’ll go over all these methods in detail. Dec 16, 2020 · Cause it is not going to be the job of React library itself to request the Unsplash API. If the data fetch is still not yet resolved, it throws a promise. In this tutorial, we will cover the most common data fetching patterns in React. In this tutorial, we’ll learn about many of Redux concepts by creating a simple React application from scratch using React, Redux and Axios to asynchronously fetch and save data to Local Storage. Logical! But not how React works. For example, your request might fail, your database might be unreachable, or your logging service might have reached its quota. fetch) and enables us to make HTTP requests very easily using JavaScript promises. Redux forces both data fetching and mutations to be imperative. I used a reducer to separate state logic and simplify testing via functional style. That’s why inputRef. See the Pen React Fetch API Pen 1 by Kingsley Silas Chijioke (@kinsomicrote) on CodePen. In case I need the state inside run function, it’s better to always use stateTuple [0] to guarantee that state points to the latest object. Then store the API URL in a variable (here api_url). Features# Composability May 24, 2021 · Basic Query. React Query + Fetch API. Assumption: You have used Create React App (CRA) to bootstrap your application The . Use fetch/ajax inside the React's useEffect method, save the result into state, and set empty array [] as the dependency. This is so you can use setState to update your component when the data is retrieved. Viewed 2 times 0 On my console log, i can see my object for my response. Below is the stepwise implementation of how we fetch the data from an API in react. The name “ SWR ” is derived from stale-while-revalidate, a cache invalidation strategy popularized by HTTP RFC 5861 . Sep 21, 2020 · Step 2 — Using Fetch to get Data from an API. json but Sep 01, 2019 · In ReactJS environment variables are fetched from . Until React 17, that name will continue to work – but this is a warning to move away from it as soon as you can. Example Apr 20, 2021 · Display API Data with React Hooks. In it, we fetch some data from an API and set state with that data. Suspense component has been shipped since React 16. The actual data object for this query and its specific query key; When fetching an uncached query, this value will be undefined Initial Query Data. Going further. For instance, JSON. To add it we need to close the running project. data will be undefined if query fails for the first time. The most accessible way to fetch data with React is using the Fetch API. The React. Jan 29, 2018 · Integrating React-native apps with back-end code using fetch API. It’s frequently referred to as just mapState for short. It's open-source, easy to use, and comes with a lot of resources already. Define a constant response and store the fetched data by await fetch () method. The useState is used to maintain the data response from the server in the component. It is called every time the store state changes. How to Fetch Data in React Using the Fetch API . Furthermore, when it comes to testing asynchronous data fetching, Sinon is helpful for spying and mocking data. Jun 15, 2018 · fetch(URL) . Note that HTTP servers often require that requests that are posted with a body also specify their type via a Content-Type request header. Data Fetching with React Hooks Introduction to React Native Fetch. Leaving the dependency to be undefined (not passing the second argument to the useEffect) will make the method inside run every Aug 16, 2021 · React Native Fetch data from api issue API , react-native / By Michael Ma I'm trying to fetch data and access it later from an api that involves token authorization. here post object will get data from axios call and it will take some time to fetch the data that means on initial render title will not be there. The idea is to get all the data from the Random User API and display it in list items inside the author’s list. Our Component. The API is consumed by our react front end app. The useFetch hook is a handy utility to retrieve data from the server and to manage network requests. json but Aug 18, 2021 · From the API we have target “id”, “name”, “username”, “email” and fetch the data from API endpoints. isIdle: boolean. React will gladly kick off an asynchronous data fetch in the background, but then it will immediately proceed with rendering – whether the data has loaded or not. Overview. env file should be in the root for you application folder. mittalyashu commented on Aug 9, 2019. The application is not very appealing, despite successfully fetching the response data. Are you read? Let's do this! 💪. The easiest way of all these different approaches to fetch data is to just use React query plus the fetch API. A very common question when building a React app is how and when data fetching will happen. It makes perfect sense to think “I want to fetch data before my component renders”. json but Use effect + React state. The most voted answer which suggests to do in componentWillMount (), a method fired off before render () in React lifecycle will be completely deprecated in React v17 (as of current writing on 5/10/2020 React is Apr 17, 2020 · Concurrent mode is experimental! Suspense for lazy-loaded components, and even simple data fetching, works today. Follow. Component class gives us a lifecycle method that makes this easy to do, and I recommend using the componentDidMount() for making any async requests that happen when the component loads. And we can use useState to handle the data fetched from the database or API. Although React’s useEffect hook allows you to do many things, In this tutorial we will walk through how to use the useEffect hook specifically to fetch data from an API, and refresh that data periodically. An auto-complete search is one example. The useEffect hook is what we used to fetch data from the server ('cos it is a side-effect) and also gives us lifecycle hooks only Note: In the future, React Hooks are not be intended for data fetching in React. /App. The following walkthrough is nonetheless a great way to learn more about state and effect hooks in React. We highly recommend it if you’re fetching data on the client side. map somewhere on this line. If it succeeds, it returns the result; otherwise, it throws In React we use className instead of class for adding a CSS class to DOM elements. When the variable is not defined, JavaScript can not read the undefined variable or property. Jul 07, 2019 · Synchronous Fetches. If something seems unfamiliar consult the React documentation. The Fetch API is a tool that's built into most modern browsers on the window object (window. The received data is saved (cached) in the application via useRef, but you can use LocalStorage (see useLocalStorage ()) or a caching solution to persist the data. stringify(data) can be used to serialize a data structure into a JSON string. But React 16. The Fetch API provides a JavaScript interface for accessing and manipulating parts of the HTTP pipeline, such as requests and responses. 8 brings Posted by Cory House July 6, 2020 July 15, 2020 3 Comments on Four Ways to Fetch Data in React React is a focused component library. Define a async function (here getapi ()) and pass api_url in that function. Define a constant data and store the data in JSON form by 2 days ago · My userData return undefined react js fetch. It depends on what is causing undefined but its at times due to:- * this binding if using classes * if you are doing data fetching in componentDidMount data will be undefined on initial render since the render method runs before componentDidMount i Feb 21, 2021 · The variable you are trying to map over is undefined. Using Fetch with a third-party API. This method can really be applied to any framework, but I’m going to explain how to do this within the context of React. The following code samples will be based on the Random User API. Now you will see the data we fetched. Introduction to React Native Fetch. Combined with the previous bit, you can be pretty sure you should be looking for .