Скачать или смотреть Tackling the ESLint Error: "Key is Not Defined" in TypeScript Classes

Discover effective solutions for the `ESLint` error regarding indexer signatures in TypeScript classes. Understand how to configure your `.eslintrc.json` to avoid such issues.
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Dealing with the ESLint "Key is Not Defined" Error in TypeScript

When working with TypeScript classes, you may come across a frustrating issue: your code runs without a hitch under the TypeScript compiler, but ESLint throws an error that can disrupt your workflow. Specifically, this error pertains to the indexer signature in your class, stating that "key is not defined." Let's dive into understanding the problem and explore viable solutions to resolve it effectively.

Understanding the Problem

Consider the following simple TypeScript class that utilizes an indexer signature:

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While this code compiles perfectly with the TypeScript compiler (tsc), ESLint raises the following error:

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This error occurs because ESLint is unable to recognize the indexer signature syntax, leading to confusion about the "key" being undefined. This is a common scenario among developers who use TypeScript alongside ESLint, especially when specific configurations are not correctly set.

Solution Overview

Fortunately, there are two straightforward approaches to eliminate this ESLint error: adjusting your ESLint configuration or modifying the rules directly. Here’s how you can go about it.

Option 1: Modify the ESLint Configuration

One effective way to get rid of the error is to modify your .eslintrc.json configuration file. Here are the steps:

Remove eslint:recommended Extend: If your project does not heavily depend on the recommended rules, you can remove the eslint:recommended extend. The google style guide may suffice for your requirements and will help avoid unnecessary conflicts.

Check the Updated Configuration: Ensure your .eslintrc.json looks somewhat like this after the change:

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Option 2: Adjust ESLint Rules

Another option is to modify a specific ESLint rule that relates to undefined variables:

Set no-undef to 0: This option tells ESLint not to enforce checks for undefined variables in your TypeScript files. You can add or modify the following rule in your configuration to achieve this:

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Although this approach is not generally recommended due to potential risks in using undefined variables, it allows TypeScript to handle the checking by itself.

Conclusion

By following either of the solutions outlined above, you can effectively resolve the ESLint error about indexer signatures in your TypeScript classes. Adjusting the configuration or modifying specific rules allows you to maintain productivity while adhering to good coding practices. Feel free to choose the approach that best suits your development needs.

In developing robust TypeScript applications, understanding how to tackle such ESLint errors will protect you from future friction in your coding journey. Happy coding!