no-unused-vars
Disallow unused variables.
Extending "plugin:@typescript-eslint/recommended"
in an ESLint configuration enables this rule.
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_
. 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
}
]
}
}
- For example, the
- 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.
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:
Options
See eslint/no-unused-vars
's options.
How to Use
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 ↗