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Linting with Type Information

Some typescript-eslint rules utilize the awesome power of TypeScript's type checking APIs to provide much deeper insights into your code. To tap into TypeScript's additional powers, there are two small changes you need to make to your config file:

.eslintrc.cjs
/* eslint-env node */
module.exports = {
  extends: [
    'eslint:recommended',
    'plugin:@typescript-eslint/recommended',
    'plugin:@typescript-eslint/recommended-type-checked',
  ],
  plugins: ['@typescript-eslint'],
  parser: '@typescript-eslint/parser',
  parserOptions: {
    project: true,
    tsconfigRootDir: __dirname,
  },
  root: true,
};
caution

Your .eslintrc.cjs file may start receiving a parsing error about type information. See our TSConfig inclusion FAQ.

In more detail:

  • plugin:@typescript-eslint/recommended-type-checked is another recommended configuration we provide. This one contains recommended rules that additionally require type information.
  • parserOptions.project tells our parser how to find the TSConfig for each source file (true indicates to find the closest tsconfig.json for each source file)
  • parserOptions.tsconfigRootDir tells our parser the absolute path of your project's root directory (see Parser#tsconfigRootDir).

With that done, run the same lint command you ran before. You may see new rules reporting errors based on type information!

Specifying TSConfigs​

The parserOptions.project option can be turned on with either:

  • true: to always use tsconfig.jsons nearest to source files
  • string | string[]: any number of glob paths to match TSConfig files relative to parserOptions.tsconfigRootDir, or the current working directory if that is not provided

For example, if you use a specific tsconfig.eslint.json for linting, you'd specify:

.eslintrc.js
module.exports = {
  // ...
  parserOptions: {
    project: './tsconfig.eslint.json',
  },
  // ...
};

See the @typescript-eslint/parser docs for more details.

note

If your project is a multi-package monorepo, see our docs on configuring a monorepo.

FAQs​

How can I disable type-aware linting for a subset of files?​

You can combine ESLint's overrides config in conjunction with our disable-type-checked config to turn off type-aware linting on specific subsets of files.

.eslintrc.js
module.exports = {
  extends: [
    'eslint:recommended',
    'plugin:@typescript-eslint/recommended',
    'plugin:@typescript-eslint/recommended-type-checked',
  ],
  plugins: ['@typescript-eslint'],
  parser: '@typescript-eslint/parser',
  parserOptions: {
    project: true,
    tsconfigRootDir: __dirname,
  },
  root: true,
  overrides: [
    {
      files: ['*.js'],
      extends: ['plugin:@typescript-eslint/disable-type-checked'],
    },
  ],
};
info

If you use type-aware rules from other plugins, you will need to manually disable these rules or use a premade config they provide to disable them.

How is performance?​

Typed rules come with a catch. By including parserOptions.project in your config, you incur the performance penalty of asking TypeScript to do a build of your project before ESLint can do its linting. For small projects this takes a negligible amount of time (a few seconds or less); for large projects, it can take longer.

Most of our users do not mind this cost as the power and safety of type-aware static analysis rules is worth the tradeoff. Additionally, most users primarily consume lint errors via IDE plugins which, through caching, do not suffer the same penalties. This means that generally they usually only run a complete lint before a push, or via their CI, where the extra time often doesn't matter.

We strongly recommend you do use type-aware linting, but the above information is included so that you can make your own, informed decision.

I get errors telling me "The file must be included in at least one of the projects provided"​

You're using an outdated version of @typescript-eslint/parser. Update to the latest version to see a more informative version of this error message, explained in our Troubleshooting and FAQs page.

Troubleshooting​

If you're having problems getting this working, please have a look at our Troubleshooting and FAQs page.