Скачать или смотреть Resolving the Cannot Read Properties of Undefined Error in React API Fetching

Learn how to fix the `TypeError` when trying to render API data in your React components using `axios` and `useState`.
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This video is based on the question https://stackoverflow.com/q/75438683/ asked by the user 'Roman' ( https://stackoverflow.com/u/21204494/ ) and on the answer https://stackoverflow.com/a/75438977/ provided by the user 'Aahan Agarwal' ( https://stackoverflow.com/u/16045352/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the Cannot Read Properties of Undefined Error in React API Fetching

When building web applications, data fetching is a common task—and it can sometimes lead to frustrating errors. One typical issue that developers encounter is the TypeError: Cannot read properties of undefined (reading map). This error often appears when attempting to map over an array that hasn't been properly set or initialized. If you're facing this issue while trying to load data from an API using React and axios, don’t worry! In this guide, we'll walk through the solutions step by step.

The Problem

You've built a news project using React and are fetching data from an API with axios. However, you're encountering an error that states:

[[See Video to Reveal this Text or Code Snippet]]

Upon inspection of your code, it seems that this error occurs when trying to map over the posts variable. Let’s explore why this might be happening and how to resolve the issue.

Understanding the Issue

In your original implementation, you’ve declared the posts variable but did not initialize it properly. This means that when you try to call .map() on it, React throws an error because posts is undefined at the moment.

Key Points:

The .map() method can only be used on an array.

If posts is not initialized as an empty array, React will throw an error when trying to access it.

The Solution

Step 1: Using useState

To solve this problem, we will introduce the useState Hook provided by React. This allows us to manage the state of posts properly and re-render the component whenever the posts state updates.

Step 2: Implementing Changes in Your Code

Below is the revised version of your component, integrating useState and ensuring that your code handles loading data correctly.

Code Example:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Made:

Initialization: const [posts, setPosts] = useState([]); initializes posts as an empty array.

Data Safety: Utilizes const data = request.data.articles || []; to ensure that if articles are not returned, it defaults to an empty array.

Using map: The posts array is now safely accessed, ensuring that the map function works without throwing errors.

Conclusion

By implementing these changes, you should eliminate the error and be able to display your fetched data seamlessly in your React application. With the power of the useState hook, managing and rendering dynamic content becomes much simpler. Happy coding!