How to Properly Populate State with All Countries in React Using useState and useEffect

Learn how to correctly add all countries to your React state without losing data using `useState` and `useEffect`.
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This video is based on the question https://stackoverflow.com/q/73934585/ asked by the user 'unknown' ( https://stackoverflow.com/u/16474818/ ) and on the answer https://stackoverflow.com/a/73934649/ provided by the user 'Mechanic' ( https://stackoverflow.com/u/5953610/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Properly Populate State with All Countries in React Using useState and useEffect

Are you struggling to add a list of countries to your state in a React application? Do you find that your state is only retaining one country instead of all of them? This is a common issue faced by many developers who are working with asynchronous data in React using hooks. In this guide, we’ll explore the problem and provide a straightforward solution for properly populating state with multiple values.

The Issue: State Retaining Only One Country

When handling API requests in React, developers often encounter issues with state management, particularly when they wish to store multiple entries. For instance, if you're trying to fetch a list of all countries from an API endpoint and store them into a state variable, you might find that only one country's name is being saved. This happens because the setState function (in this case, getCountry) is being called multiple times, replacing the previous state with the new one, rather than merging them.

Sample Code That Causes the Problem

Here's an example of code that can lead to this issue:

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

In the above example, each call to getCountry replaces the current state with a new country name. Therefore, by the time the loop completes, the state will only reflect the last country processed.

The Solution: Map the Data Correctly

To fix this issue, you can utilize the map function to create an array of all country names and then set that array in one go. This way, instead of setting one country at a time, you'll gather all the country names and update the state with the full array at once.

Here’s the Correct Approach

You can modify the .then part of your code as follows:

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

Explanation of the Solution

Using map(): The map function iterates through the response.data array, transforming each country object into its official name and producing a new array of country names.

Setting State Once: By calling getCountry with the entire array of names (response.data.map(...)), we effectively set the state once, ensuring that all country names are saved together in the state variable.

Conclusion

In conclusion, when working with API data in React, especially when utilizing hooks like useState and useEffect, it's crucial to understand how state updates work. By leveraging the power of map, you can seamlessly collect multiple values and set them in your component's state without losing any data.

If you're still facing challenges while dealing with API data in React, feel free to reach out or leave a comment below. Happy coding!

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