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no-unused-vars.md

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description
Disallow unused variables.

🛑 This file is source code, not the primary documentation location! 🛑

See https://typescript-eslint.io/rules/no-unused-vars for documentation.

This rule extends the base eslint/no-unused-vars rule. It adds support for TypeScript features, such as types.

Benefits Over TypeScript

TypeScript provides noUnusedLocals and noUnusedParameters compiler options that can report errors on unused local variables or parameters, respectively. Those compiler options can be convenient to use if you don't want to set up ESLint and typescript-eslint. However:

  • These lint rules are more configurable than TypeScript's compiler options.
    • For example, the varsIgnorePattern option can customize what names are always allowed to be exempted. TypeScript hardcodes its exemptions to names starting with _.
  • ESLint can be configured within lines, files, and folders. TypeScript compiler options are linked to their TSConfig file.
  • Many projects configure TypeScript's reported errors to block builds more aggressively than ESLint complaints. Blocking builds on unused variables can be inconvenient.

We generally recommend using @typescript-eslint/no-unused-vars to flag unused locals and parameters instead of TypeScript.

:::tip Editors such as VS Code will still generally "grey out" unused variables even if noUnusedLocals and noUnusedParameters are not enabled in a project. :::