Скачать или смотреть How to Fix setState Issues Inside Axios Calls in ReactJS

Struggling with accessing `setState` in Axios calls? This guide explains the issue and how to resolve it using arrow functions in ReactJS.
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This video is based on the question https://stackoverflow.com/q/72034247/ asked by the user 'Alex Furdui' ( https://stackoverflow.com/u/14909662/ ) and on the answer https://stackoverflow.com/a/72034480/ provided by the user 'Som Shekhar Mukherjee' ( https://stackoverflow.com/u/11719314/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue with setState in Axios Calls in ReactJS

If you've been working on a ReactJS application and found yourself facing the error Cannot read properties of undefined (reading 'setState') inside an Axios call, you’re not alone. This is a common issue, particularly among developers using class-based components. Let’s dive in and explore the reasons behind this problem and how to solve it effectively.

The Problem Explained

When you make an API call using Axios and attempt to update the component's state using setState, you might encounter unexpected behaviors related to the this context. Here's a simplified flow of what's happening:

Callback Context: In JavaScript, the value of this can change based on how a function is invoked. In regular functions (non-arrow functions), this may not refer to the class instance unless it’s specifically bound.

Default Behavior of this: In strict mode, this can become undefined. In non-strict mode, this defaults to the global object. This can lead to errors when you try to access methods or properties that are meant to belong to your component.

For instance, when you declare your Axios call as follows:

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

In this standard function, this does not point to the component class, leading to the mentioned error.

The Solution: Use Arrow Functions

The best way to avoid this issue is to switch from a regular function to an arrow function. Arrow functions do not have their own this context. Instead, they lexically bind this based on the context in which they were defined.

Here’s the revised code:

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

Why This Works

Lexical Scope: By using an arrow function, this will retain the context of the surrounding lexical scope, which in this case is your React component.

No More Errors: This change will eliminate the error you were encountering, allowing you to successfully update your state based on the response from the Axios call.

Conclusion

In ReactJS, particularly when working with class-based components, handling function context with this can be tricky, especially in asynchronous calls such as those made with Axios. By consistently using arrow functions in your promises and callbacks, you can avoid errors and ensure that this refers to your class instance.

If you ever find yourself getting confused about this, remember that arrow functions are your friend in these scenarios! Hopefully, this guide has helped clarify the issue and provided a straightforward solution.