Lykn

External Linters: When You Need Them

Deno’s built-in tools and lykn lint are the default. ESLint and Biome are optional tools for projects with specific JavaScript-side needs.

When to Reach for External Linters

• Framework-specific JavaScript plugins: React, Vue, Angular, and their cousins in increasingly elaborate hats
• Organizational standards that already require ESLint
• Custom JavaScript lint rules Deno does not support
• Very large generated or hand-written JS codebases where Biome’s speed matters

ESLint for Lykn Output

Flat config (eslint.config.js):

export default [
  {
    ignores: ["target/lykn/**"],
    rules: {
      "eqeqeq": ["error", "smart"],
      "no-unused-vars": ["warn", { "argsIgnorePattern": "^_" }],
      "prefer-const": "error",
    }
  }
];

The "smart" option for eqeqeq allows == null while enforcing === elsewhere. That matters because Lykn intentionally emits nullish checks in a few places where JavaScript’s loose-null idiom is the correct spell.

Biome

Biome is a fast standalone formatter and linter. Use it if your project already standardizes on Biome or needs one binary outside Deno’s toolchain. For ordinary Lykn projects, start with lykn lint, lykn fmt, deno lint, and deno fmt.

The Recommendation

Do not start by installing a second linting ecosystem. Start with Lykn’s source linter and Deno’s built-ins. Add ESLint or Biome when a concrete JavaScript requirement appears, and keep generated target/lykn/ output out of source-style policy unless that policy is intentionally about compiler output.