no-unused-vars

Disallow unused variables.

✅

Extending "plugin:@typescript-eslint/recommended" in an ESLint configuration enables this rule.

🧱

This is an "extension" rule that replaces a core ESLint rule to work with TypeScript. See Rules > Extension Rules.

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

How to Use

Flat Config

eslint.config.mjs

export default tseslint.config({
  rules: {
    // Note: you must disable the base rule as it can report incorrect errors
    "no-unused-vars": "off",
    "@typescript-eslint/no-unused-vars": "error"
  }
});

Legacy Config

.eslintrc.cjs

module.exports = {
  "rules": {
    // Note: you must disable the base rule as it can report incorrect errors
    "no-unused-vars": "off",
    "@typescript-eslint/no-unused-vars": "error"
  }
};

Try this rule in the playground ↗

Options

See eslint/no-unused-vars's options.

FAQs

What benefits does this rule have 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 _. If you would like to emulate the TypeScript style of exempting names starting with _, you can use this configuration (this includes errors as well):

    {
      "rules": {
        "@typescript-eslint/no-unused-vars": [
          "error",
          {
            "args": "all",
            "argsIgnorePattern": "^_",
            "caughtErrors": "all",
            "caughtErrorsIgnorePattern": "^_",
            "destructuredArrayIgnorePattern": "^_",
            "varsIgnorePattern": "^_",
            "ignoreRestSiblings": true
          }
        ]
      }
    }
• 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.

Also see similar rules provided by ESLint:

• no-unused-private-class-members
• no-unused-labels

Why does this rule report variables used only for types?

This rule does not count type-only uses when determining whether a variable is used. Declaring variables only to use them for types adds code and runtime complexity. The variables are never actually used at runtime. They can be misleading to readers of the code.

typeof Variables

For example, if a variable is only used for typeof, this rule will report:

const box = {
  //  ~~~
  //  'box' is assigned a value but only used as a type.
  value: 123,
};

export type Box = typeof box;

Open in Playground

Instead, it's often cleaner and less code to write out the types directly:

export interface Box {
  value: number;
}

Open in Playground

Zod Schemas

For example, if a Zod schema variable is only used for typeof, this rule will report:

import { z } from 'zod';

const schema = z.object({
  //  ~~~~~~
  //  'schema' is assigned a value but only used as a type.
  value: z.number(),
});

export type Box = z.infer<typeof schema>;

Open in Playground

Instead, it's often cleaner and less code to write out the types directly:

export interface Box {
  value: number;
}

Open in Playground

If you find yourself writing runtime values only for types, consider refactoring your code to declare types directly.

Resources

• Rule source
• Test source

^{Taken with ❤️ from ESLint core.}