TypeScript Language Guide¶

linthis uses eslint for linting and prettier for formatting TypeScript code.

Supported File Extensions¶

.ts
.tsx
.mts
.cts

Required Tools¶

Linter: eslint¶

# Install globally
npm install -g eslint

# Or project-local
npm install --save-dev eslint

# For TypeScript support
npm install --save-dev @typescript-eslint/parser @typescript-eslint/eslint-plugin

# Verify installation
eslint --version

Formatter: prettier¶

# Install globally
npm install -g prettier

# Or project-local
npm install --save-dev prettier

# Verify installation
prettier --version

Configuration¶

Basic Example¶

# .linthis/config.toml

[typescript]
max_complexity = 15
excludes = ["dist/**", "node_modules/**", "*.d.ts"]

Disable Specific Rules¶

[typescript.rules]
disable = [
    "@typescript-eslint/no-explicit-any",
    "@typescript-eslint/no-unused-vars",
    "no-console"
]

Change Severity¶

[typescript.rules.severity]
"@typescript-eslint/no-unsafe-assignment" = "error"
"@typescript-eslint/explicit-function-return-type" = "warning"

Custom Rules¶

[[rules.custom]]
code = "ts/no-console-log"
pattern = "console\\.log"
message = "Remove console.log before committing"
severity = "warning"
suggestion = "Use a proper logging library"
languages = ["typescript"]

[[rules.custom]]
code = "ts/no-any-cast"
pattern = "as any"
message = "Avoid 'as any' type assertions"
severity = "warning"
languages = ["typescript"]

CLI Usage¶

# Check TypeScript files only
linthis -c --lang typescript

# Format TypeScript files only
linthis -f --lang typescript

# Check specific file
linthis -c src/index.ts

ESLint Configuration¶

linthis uses your project's ESLint configuration. Create .eslintrc.json:

{
  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint"],
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended"
  ],
  "rules": {
    "@typescript-eslint/no-unused-vars": "warn",
    "@typescript-eslint/explicit-function-return-type": "off"
  }
}

Or use flat config (eslint.config.js):

import tseslint from '@typescript-eslint/eslint-plugin';
import tsparser from '@typescript-eslint/parser';

export default [
  {
    files: ['**/*.ts', '**/*.tsx'],
    languageOptions: {
      parser: tsparser,
    },
    plugins: {
      '@typescript-eslint': tseslint,
    },
    rules: {
      ...tseslint.configs.recommended.rules,
    },
  },
];

Prettier Configuration¶

Create .prettierrc:

{
  "semi": true,
  "singleQuote": true,
  "tabWidth": 2,
  "trailingComma": "es5",
  "printWidth": 100
}

Common Issues¶

ESLint not finding TypeScript config¶

Ensure you have the TypeScript ESLint packages installed:

npm install --save-dev @typescript-eslint/parser @typescript-eslint/eslint-plugin

Prettier and ESLint conflicts¶

Use eslint-config-prettier to disable formatting rules in ESLint:

npm install --save-dev eslint-config-prettier

Then add to .eslintrc.json:

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

Type declaration files being checked¶

Add to excludes:

[typescript]
excludes = ["*.d.ts", "**/*.d.ts"]

Best Practices¶

Use strict TypeScript: Enable strict: true in tsconfig.json
ESLint + Prettier: Use both together with eslint-config-prettier
Type-aware linting: Enable type-aware rules for better checking
Consistent formatting: Let prettier handle all formatting, disable ESLint formatting rules