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Add note about not needing jsx-no-undef with TS / typescript-eslint #3941

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Add note about not needing jsx-no-undef with TS / typescript-eslint #3941

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a55b5c2
Add note about not needing jsx-no-undef with typescript-eslint
karlhorky Aug 3, 2025
1148271
Fix link
karlhorky Aug 3, 2025
b85d541
Add note about TypeScript
karlhorky Aug 9, 2025
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6 changes: 5 additions & 1 deletion docs/rules/jsx-no-undef.md
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Expand Up @@ -58,4 +58,8 @@ module.exports = Hello;

## When Not To Use It

If you are not using JSX then you can disable this rule.
It's recommended to avoid this rule if your project:

1. does not use JSX
2. uses TypeScript, which [automatically enables better checks than ESLint `no-undef` rules](https://typescript-eslint.io/troubleshooting/faqs/eslint/#i-get-errors-from-the-no-undef-rule-about-global-variables-not-being-defined-even-though-there-are-no-typescript-errors)
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item 2 and 3 are basically the same - it would be a very bad idea to turn off this rule and NOT enable the typescript-eslint rule.

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@karlhorky karlhorky Aug 13, 2025 •
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Hmm, well following the advice from the typescript-eslint docs, actually the no-undef rule should be disabled in TypeScript files

So option 3 is for files where TS type checking is disabled, eg. JS files in a typescript-eslint project

If that doesn't make sense, I can try re-explaining

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ah, hmm, ok - which version of TS enabled these better checks? (because TS definitely did not used to do a better job than this rule)

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Good question, I'm thinking that this was like this from pretty early on... can't remember a time when TS didn't give me errors for undefined JSX element identifiers 🤔

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the TS playground goes back to version 3.3.3333, and it seems like it's present there:

Screenshot 2025-08-13 at 19 38 55

https://www.typescriptlang.org/play/?ts=3.3.3#code/JYWwDg9gTgLgBAJQKYEMDG8BmUIjgcilQ3wG4AoSygHgAkkAbBiOAOxRCQF4AiAKQgALVjzgB6AHykgA

3. uses [`typescript-eslint` with `no-undef`](https://typescript-eslint.io/play/#ts=5.7.2&fileType=.tsx&code=DwCQpgNhD2AEB2BDAtmAvAIgFLQBbw1gHoA%2BAbgCgg&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQHYHsBaWXAE0QDN0pFpp9pJwwBfEFoA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=false)
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