ESLint - Configuring "no-unused-vars" for TypeScript

It's a bit buried in the documentation, but if you add some things to the 'extends' property, you can use both the rules recommended by ESLint like no-unused-vars, and have it actually work in Typescript. Like so:

"extends": [
        "eslint:recommended",
        "plugin:@typescript-eslint/eslint-recommended",
        "plugin:@typescript-eslint/recommended"
    ],

@typescript-eslint/recommended seems to be the thing that allows eslint:recommended to deal with Typescript constructs effectively. Not sure how it would affect your other extensions though.

I think the use of "plugin:@typescript-eslint/eslint-recommended" introduces bunch of unwanted rules. One is probably better off using "@typescript-eslint/no-unused-vars" ESLint rule instead.

{
  "parser": "@typescript-eslint/parser",
  "plugins": [
    "@typescript-eslint",
  ],
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended",
  ],
  "rules": {
    "no-unused-vars": "off",
    "@typescript-eslint/no-unused-vars": ["error"]
  }
}

Reference - https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-unused-vars.md

I got lot of false errors with latest TypeScript/ES-Lint versions and I found that they came up with an experimental rule to fix the no-unused-vars which is broken and with the experimental rule @typescript-eslint/no-unused-vars-experimental it finally works as I expect it to.

Prior to the change on my side, I had multiple false errors when using interfaces/types saying that these vars were unused (which of course they'll never be used since they're not variables but rather interfaces/types)... and in case you're curious about the code itself, here is the PR adding this experimental rule which is how I found the rule.

Here's a subset of my updated .eslintrc file

{
  "parser": "@typescript-eslint/parser",
  "extends": [
    "plugin:@typescript-eslint/recommended"
  ],
  "rules": {
    "@typescript-eslint/no-unused-vars": "off",
    "@typescript-eslint/no-unused-vars-experimental": "error",
    "no-unused-vars": "off"
  }
}

and I'm now finally back to normal :)

EDIT (Jan. 2021)

As mentioned by Brad (a maintainer of the project) in the comment below, this is (was) a temporary solution and is now deprecated. From his comment (below), we can now use directly @typescript-eslint/no-unused-vars for the same intended behavior. Thanks to Brad for the info. I can also confirm that switching back to @typescript-eslint/no-unused-vars now works for me (I updated my code and it's all good now).

This is not the way to go, and you should avoid it. @typescript-eslint/no-unused-vars-experimental is deprecated, and will be removed in the next major. Update to the latest version of the tooling and just use @typescript-eslint/no-unused-vars. Source: I am the maintainer of the project.

So here's the latest update of my .eslintrc file which works for me :)

{
  "parser": "@typescript-eslint/parser",
  "extends": [
    "plugin:@typescript-eslint/recommended"
  ],
  "rules": {
    "@typescript-eslint/no-unused-vars": "error",
    "no-unused-vars": "off"
  }
}

My issue was with using decorators and wanting to have a variable with an appropriate name for clarity, for example:

@OneToMany((type) => Employee) instead of @OneToMany(() => Employee)

The usual solution for TypeScript is to prefix with an underscore:

@OneToMany((_type) => Employee)

And it's possible to make ESLint accept the same:

.eslintrc.js

module.exports = {
  ...
  rules: {
    '@typescript-eslint/no-unused-vars': ['warn', { 'argsIgnorePattern': '^_' }]
    ....
  },
};

You have parser nested inside of parserOptions. It should be a sibling, like this:

"parser": "@typescript-eslint/parser",
"parserOptions": {
    "ecmaVersion": 2018,
    "sourceType": "module"
},

As for no-unused-vars, I'm afraid this is an ongoing bug with @typescript-eslint: https://github.com/typescript-eslint/typescript-eslint/issues/363

Upgrading @typescript-eslint/eslint-plugin and @typescript-eslint/parser from 3.x to the latest 4.x resolved the issue for me.

Also for me works rule /eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]/ You can add it like this in your .eslintrc.json file (this one is for ignoring all Strings which start with Capital letter)

    "rules": {
        "no-unused-vars": [
          "error",
          {
            "varsIgnorePattern": "^[A-Z]"
          }
        ],
    }

For more information, and properties you can check this link.

After couple of year still getting the same error. It's frustrate to try and check why it's not working. After trying lot of possible configuration here is the finally working for me. Incase someone had difficulties like me !

eslintrc.js

module.exports = {
    env: {
        browser: true,
        node: true,
    },
    parser: "@typescript-eslint/parser",
    extends: [
        "eslint:recommended",
        "plugin:@typescript-eslint/eslint-recommended",
        "prettier",
        "plugin:prettier/recommended",
        "plugin:@typescript-eslint/recommended",
    ],
    parserOptions: {
        ecmaVersion: 2020, // Allows for the parsing of modern ECMAScript features
        project: "tsconfig.eslint.json",
        tsconfigRootDir: __dirname,
        sourceType: "module", // Allows for the use of imports
    },
    plugins: ["@typescript-eslint", "@typescript-eslint/tslint", "import", "unused-imports"],

    rules: {
        "@typescript-eslint/no-unused-vars": "off",
        "@typescript-eslint/no-unused-vars-experimental": "error",
        "no-unused-vars": "off",
        "import/order": "error",
        "no-console": ["warn", { allow: ["warn", "error"] }],
        eqeqeq: ["error", "always"],
        "no-else-return": "error",
    },
    settings: {
        "import/resolver": {
            node: {
                extensions: [".js", ".jsx", ".ts", ".tsx"],
                moduleDirectory: ["node_modules", "src/"],
            },
        },
    },
};

For anyone looking to get no-unused-vars working properly in TypeScript when using YAML configuration, e.g. .eslintrc.yaml, it looks like this:

rules:

  "@typescript-eslint/no-unused-vars":
  - warn
  - argsIgnorePattern: "^_"                # <-- NOTE!
    varsIgnorePattern: "^_"
    caughtErrorsIgnorePattern: "^_"

  no-unused-vars: # disabled but see typescript-eslint/no-unused-vars
  - off
  ...