Cheminfo ESLint TypeScript Configuration

Common errors

• Error: Failed to load config "cheminfo-typescript" to extend from. Referenced from: ...

  cause ESLint cannot find the configuration package because it's either not installed or the import path is incorrect.
  fix Ensure `eslint-config-cheminfo-typescript` is installed (`npm i -D eslint-config-cheminfo-typescript`) and the import path in `eslint.config.mjs` is `import cheminfo from 'eslint-config-cheminfo-typescript';`.

• ESLint: Cannot read properties of undefined (reading 'eslint') TypeError: Cannot read properties of undefined (reading 'eslint')

  cause This error often occurs when `eslint-plugin-typescript` (or related plugins) cannot find the TypeScript parser or `tsconfig.json`.
  fix Verify `typescript` is installed and that your `eslint.config.mjs` includes `languageOptions: { parserOptions: { project: './tsconfig.json' } }` correctly configured for your project.

• ESLint: Cannot read config file: ...eslint.config.mjs

  cause ESLint is unable to parse or find the configuration file, possibly due to incorrect file extension, syntax errors, or module type issues.
  fix Ensure your config file is named `eslint.config.mjs` (or `.js` with `"type": "module"` in `package.json`), contains valid JavaScript/ESM syntax, and is accessible to ESLint.

• ESLint: Rule 'no-redeclare' was removed and replaced by 'no-redeclare' in @typescript-eslint/eslint-plugin.

  cause A common conflict or deprecation when using TypeScript ESLint plugins, where the base ESLint rule is replaced by a type-aware version.
  fix This specific rule was fixed in v21.0.1. If on an older version, update the package. Otherwise, ensure no custom rules conflict by re-enabling `@typescript-eslint/no-redeclare` if needed, or remove the rule entirely if it's implicitly handled.

Warnings

• breaking All configurations now strictly require the ESLint Flat Config format. Traditional `.eslintrc.*` files are no longer supported.
  Fix: Migrate your ESLint setup to use `eslint.config.mjs` (or `.js` with `type: 'module'`) and follow the flat config migration guide linked in the package README.
• breaking The package frequently updates its peer dependency for `eslint`. Ensure your `eslint` version meets the minimum requirement specified in `peerDependencies` to avoid compatibility issues.
  Fix: Update your `eslint` package to the version specified in the `peerDependencies` of `eslint-config-cheminfo-typescript` (e.g., `npm i -D eslint@^9.39.1`).
• breaking Major versions often introduce breaking changes by updating the base JavaScript config, underlying ESLint plugins, or ESLint itself, leading to new rules or changes in existing ones.
  Fix: Review the release notes for each major version update. Run ESLint after updating and address any new errors or warnings. Consider using an ESLint `--fix` dry run first.
• gotcha The configuration relies on `typescript` being installed and correctly configured in your project's `tsconfig.json` for type-aware linting rules to function.
  Fix: Ensure `typescript` is installed (`npm i -D typescript`) and your `eslint.config.mjs`'s `languageOptions.parserOptions.project` points to your `tsconfig.json`.
• breaking Version 22.0.0 specifically updates the base config to v18, which may introduce new linting rules or modify existing rule severities inherited from the JavaScript base configuration.
  Fix: Examine the `eslint-config-cheminfo` v18 release notes for specific changes. Address any newly reported linting issues in your codebase.

Install

• npm install eslint-config-cheminfo-typescript npm
• yarn add eslint-config-cheminfo-typescript yarn
• pnpm add eslint-config-cheminfo-typescript pnpm

Imports

• cheminfo
  wrong:

  const cheminfo = require('eslint-config-cheminfo-typescript');

  correct:

  import cheminfo from 'eslint-config-cheminfo-typescript';

  This config is designed for ESM and ESLint's flat config. `require` is generally not supported for direct import.
• cheminfo.base
  wrong:

  import { base } from 'eslint-config-cheminfo-typescript';

  correct:

  import cheminfoBase from 'eslint-config-cheminfo-typescript/base';

  Specific sub-configurations are imported via direct path, not as named exports from the main package.
• defineConfig
  wrong:

  import defineConfig from 'eslint/config';

  correct:

  import { defineConfig } from 'eslint/config';

  ESLint's `defineConfig` utility is a named export from `eslint/config` and is crucial for proper flat config setup.

Quickstart

This quickstart demonstrates how to set up `eslint-config-cheminfo-typescript` in an `eslint.config.mjs` file, importing the default configuration and showing how to extend or override rules for a specific project.

import { defineConfig } from 'eslint/config';
import cheminfo from 'eslint-config-cheminfo-typescript';

export default defineConfig(
  // Apply the base Cheminfo TypeScript config
  cheminfo,
  {
    // Example: Override or add project-specific rules
    rules: {
      'no-console': 'warn',
      'prefer-const': 'error'
    },
    // Example: Target specific files
    files: ['src/**/*.ts', 'test/**/*.ts'],
    // Example: Configure parser options for specific environments
    languageOptions: {
      parserOptions: {
        project: './tsconfig.json'
      }
    }
  }
);