Adding eslint and Auto-Fixing an Existing TypeScript Project

In opensearch-api-specification#260 I added eslint, but had a hard time finding a cookbook for auto-fixing specific violations. Here it is.

First, I followed the getting started with eslint guide, which essentially tells you to run npm init @eslint/config@latest.

Rewrite eslint.config.mjs using the newer flat configuration format, making sure that the ignores and rules section appears last, as it will overwrite the defaults. For my TypeScript project, see the complete file here.

export default [
  pluginJs.configs.recommended,
  ...compat.extends('standard-with-typescript'),
  {
    files: ['**/*.{js,ts}'],
    ignores: [
      ...
    ],
    rules: {
      ...
    }
  }
]

Add the linter to scripts.

"scripts": {
  "lint": "eslint .",
}

Run the linter with npm run lint. My first run resulted in a lot of violations. I exctracted the list of them with jq and pasted it into rules.

$ npm run --silent lint -- --format json | jq '.[].messages[] | select(.line != null) .ruleId' | sort | uniq

export default [
  pluginJs.configs.recommended,
  ...compat.extends('standard-with-typescript'),
  {
    rules: {
      '@typescript-eslint/consistent-indexed-object-style': 'warn',
      '@typescript-eslint/consistent-type-assertions': 'warn',
      '@typescript-eslint/dot-notation': 'warn',
      ...
    }
  }
]

Now, npm run lint will execute successfully showing warnings only.

../tools/test/linter/factories/schema_file.ts
   4:17  warning  Function name `schema_file` must match one of the following formats: camelCase, PascalCase, UPPER_CASE         @typescript-eslint/naming-convention
  10:32  warning  void is not valid as a constituent in a union type                                                             @typescript-eslint/no-invalid-void-type

To auto-fix, first disable all rules with off and enable the one you want to auto-fix with error.

export default [
  pluginJs.configs.recommended,
  ...compat.extends('standard-with-typescript'),
  {
    rules: {
      '@typescript-eslint/consistent-indexed-object-style': 'off',
      '@typescript-eslint/consistent-type-assertions": 'off',
      '@typescript-eslint/dot-notation": 'error',
    }
  }
]

Now run npm run lint -- --fix. Not all rules have an autofixer, but if yours does it will make the code changes, and you can now remove if rom the config and finally turn back all other rules to warn.

Here’s my second pull request that fixed most self-correcting violations.

A word of caution, beware of --fix. In the project above the dot-notation autofix made a destructive change that caused tests to fail (and that I have yet to debug).

Daniel Doubrovkine

Adding eslint and Auto-Fixing an Existing TypeScript Project opensearch | javascript

Adding eslint and Auto-Fixing an Existing TypeScript Project