Resolving the TypeError: Cannot read property 'setState' of undefined in React

Discover how to fix the `Cannot read property 'setState' of undefined` error in your React application. This guide provides clear solutions to manage function scope issues in your components.
---
This video is based on the question https://stackoverflow.com/q/64275981/ asked by the user 'Pim_vh' ( https://stackoverflow.com/u/12302390/ ) and on the answer https://stackoverflow.com/a/64276401/ provided by the user 'Peter Lehnhardt' ( https://stackoverflow.com/u/5312110/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: React Cannot read property 'setState' of undefined in if-block

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the TypeError: Cannot read property 'setState' of undefined in React

If you're diving into React and have encountered the error message TypeError: Cannot read property 'setState' of undefined, you're not alone. This error often arises when dealing with class-based components, especially when invoking methods within certain code blocks, like if-statements. In this post, we'll break down the causes of this error and present two effective solutions to keep your React application running smoothly.

The Problem

In React, each class component has a context (this) that refers to the component instance. However, when you define functions within a class, the binding for this can behave unexpectedly. In the provided code, the issue occurs when calling setState inside an if-block. Specifically, this leads to the error because this is not bound to the component instance within the functions.

Example Code Snippet

Here is the code snippet that triggers the error:

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

Solutions to the Problem

Fortunately, there are two straightforward ways to solve this issue so that you can use this.setState without errors.

Solution 1: Use Arrow Functions

Arrow functions automatically bind this to the context in which they were defined, meaning they retain the correct reference to the component instance. Here's how you can implement this:

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

By defining your functions as arrow functions, this will always refer to your component instance, and you will avoid the error.

Solution 2: Manually Bind this in the Constructor

If you'd rather keep your traditional function definitions, you can explicitly bind this in the constructor of your component. Here's how you would do that:

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

With this approach, this inside getFilteredTrades and getAllTrades will correctly reference the component instance.

Conclusion

Both solutions above will resolve the TypeError: Cannot read property 'setState' of undefined issue in your React application. Choose either the arrow function approach or the manual binding method based on your style preference, and keep building your amazing React components without any obstacles!

If you found this information helpful, feel free to share it with your fellow developers who may encounter the same issue. Happy coding!