untodo

Type-safe TODO for humans and AI — trackable, structured, and lint-enforceable.

Type-safe replacement for // TODO: comments. Trackable in your IDE, enforceable by lint, surfaced by the type system.

Status: scaffold — APIs are placeholders. See Project Planning in the repo for the design.

Why

Problem	Solution
// TODO: comments are easy to ignore	Function calls — lint can fail the build
Comments don't reach the type system	Returns never so callers detect it
No structure	Pass an object with reason, issue, etc.
Hard to track in an IDE	"Find references" works on a function

Inspired by Kotlin's TODO().

Affinity with AI coding assistants

Now that AI-assisted coding is the norm, // TODO: comments have a new set of problems. AI reads comments as plain text, so it tends to miss the fact that a TODO exists, and the way TODOs are written drifts from author to author.

untodo addresses both issues.

AI recognizes TODOs more reliably

A TODO in untodo is a function call backed by a type definition. AI coding assistants (Claude, GitHub Copilot, etc.) take type information and function signatures into account as context, so they pick up the existence and intent of a TODO far more reliably than from a // TODO: comment.

// AI sees this only as "text"
// TODO: implement later (where? who? why?)

// AI sees this as "a call to an unimplemented function"
return TODO({ reason: "API not implemented yet", issue: 123, assignee: "alice" })

Structured metadata like reason, issue, and assignee lets AI accurately read off who left the TODO, why, and which issue it is tied to.

TODOs become consistent in style

// TODO: comments tend to be written differently by every author.

// TODO: fix this
// TODO(alice): fix later
// TODO #123
// FIXME: has a bug

With untodo, ESLint / oxlint rules can ban comment-style TODOs and enforce the function-call form. Consistent shape also improves AI completion and suggestion quality when it reads the surrounding code.

Install

npm install untodo

Quick start

Run the bundled initializer once at the project root:

npx untodo init

This writes two files (and prints an ESLint snippet you can paste into your existing config). Existing files are skipped unless you pass --force.

wrote: ./untodo.config.ts
wrote: ./global.d.ts

1. untodo.config.ts — runtime configuration

Registers project-wide defaults via defineConfig. Per-call callbacks passed to TODO() / FIXME() / HACK() always win over what's set here, so this file is the right place to put fallback behavior.

The generated template ships with everything commented out:

import { defineConfig } from 'untodo';

export default defineConfig({
  // repo: 'org/repo',
  // onTodo:  (meta) => console.warn(`TODO: ${meta.reason}`),
  // onFixme: (meta) => console.error(`FIXME: ${meta.reason}`),
  // onHack:  (meta) => console.warn(`HACK: ${meta.reason}`),
});

Field	Type	Purpose
repo	string	Repository in org/repo form. Tooling uses it to expand the issue meta field into a full URL (e.g. https://github.com/org/repo/issues/123).
onTodo	(meta: TodoMeta) => void	Default handler for every TODO() call that doesn't pass its own callback.
onFixme	(meta: FixmeMeta) => void	Default handler for every FIXME() call that doesn't pass its own callback.
onHack	(meta: HackMeta) => void	Default handler for every HACK() call that doesn't pass its own callback.

A typical setup that warns in development and integrates with your logger:

import { defineConfig } from 'untodo';

export default defineConfig({
  repo: 'ysknsid25/untodo',
  onTodo: (meta) => {
    const issue = meta.issue ? ` (#${meta.issue})` : '';
    console.warn(`TODO${issue}: ${meta.reason}`);
  },
  onFixme: (meta) => console.error(`FIXME: ${meta.reason}`),
  onHack:  (meta) => console.warn(`HACK: ${meta.reason}`),
});

Import this file once from your application entry point (or test setup) so defineConfig runs before any TODO() is evaluated:

import './untodo.config';

2. global.d.ts — extending the meta types

TODO(), FIXME(), and HACK() accept structured metadata. By default only reason: string is required. Add project-specific fields to the TodoMeta / FixmeMeta / HackMeta interfaces via TypeScript Declaration Merging.

The generated template:

declare module 'untodo' {
  interface TodoMeta {
    // issue?: number | string;
    // assignee?: string;
  }
  interface FixmeMeta {
    // issue?: number | string;
  }
  interface HackMeta {
    // issue?: number | string;
  }
}

export {};

Uncomment or add fields to fit your team's workflow. For example:

declare module 'untodo' {
  interface TodoMeta {
    issue?: number | string;
    assignee?: string;
    severity?: 'low' | 'medium' | 'high';
  }
  interface FixmeMeta {
    issue?: number | string;
  }
  interface HackMeta {
    issue?: number | string;
  }
}

export {};

After this, callers get full type checking and IDE autocomplete for the extra fields:

return TODO({
  reason: 'wire up the user repository',
  issue: 123,           // ← typed
  assignee: 'alice',    // ← typed
  severity: 'high',     // ← typed, only 'low' | 'medium' | 'high' allowed
});

Make sure global.d.ts is included by your tsconfig.json (most default "include" patterns already pick up **/*.d.ts).

The trailing export {}; keeps the file as a module, which is required for declare module augmentation to apply.

3. Add the ESLint plugin

init finishes by printing a flat-config snippet. Paste it into your existing eslint.config.ts (or .mjs):

import untodoPlugin from 'untodo/eslint';

export default [
  {
    plugins: { untodo: untodoPlugin },
    rules: {
      'untodo/no-todo':  'error',
      'untodo/no-fixme': 'error',
      'untodo/no-hack':  'warn',
    },
  },
];

The same plugin works with oxlint's JS plugin support.

Usage

import { TODO, FIXME, HACK } from 'untodo';

function fetchUser(): User {
  return TODO({ reason: 'wire up the user repository' });
}

function parseDate(input: string): Date {
  return FIXME({ reason: 'rejects valid ISO strings with offsets' });
}

function legacyAdapter(): Adapter {
  return HACK({ reason: 'old API ships in the next major; remove then' });
}

Because each function returns never, the surrounding code keeps type-checking as if a real value flowed through — there's no need to add as User casts or fake return values.

Per-call handlers

Pass a callback as the second argument to override the global handler for one call:

return TODO(
  { reason: 'wire up the user repository' },
  (meta) => myLogger.warn('todo.hit', meta),
);

Opting out of the global handler

Once defineConfig({ onTodo }) is set, every TODO() call without a per-call callback fires the global handler. That's usually what you want — but on a hot path, or for a deliberately quiet placeholder, you may want one specific call to skip the handler.

untodo does not bake an opt-out flag into the meta types — naming and semantics are policy, and policy belongs to your team. The recommended pattern is to add a boolean field via Declaration Merging and short-circuit inside your handler:

// global.d.ts — pick whatever name your team prefers (silent / muted / skip ...)
declare module 'untodo' {
  interface TodoMeta {
    silent?: boolean;
  }
}

// untodo.config.ts
import { defineConfig } from 'untodo';

export default defineConfig({
  onTodo: (meta) => {
    if (meta.silent) return;
    sendToSentry(meta);
  },
});

// usage
TODO({ reason: 'normal placeholder' });                  // global fires
TODO({ reason: 'tight loop', silent: true });            // global skipped
TODO({ reason: 'custom path' }, (m) => myLogger.warn(m)); // per-call wins, global skipped

The same pattern applies to FixmeMeta / HackMeta. Keeping the gate inside the handler — rather than as a library-level switch — means the predicate can be as nuanced as you need (if (meta.severity === 'low' && process.env.CI) return; etc.) without untodo having to anticipate every shape.

API

Export	Description
TODO(meta, cb?)	Marks a code path as not yet implemented. Returns never.
FIXME(meta, cb?)	Marks broken code that must be repaired. Returns never.
HACK(meta, cb?)	Marks a deliberate workaround to revisit. Returns never.
defineConfig(config)	Registers project-wide defaults (used in untodo.config.ts).
untodo/eslint	ESLint / oxlint plugin exposing no-todo, no-fixme, no-hack rules.

None of TODO / FIXME / HACK throw at runtime — they only invoke the configured handler. Lint enforcement is what makes them block the build.

Bundle size

Trading // TODO: comments for function calls is not free. Comments are stripped by minification; function calls survive it, so every call site keeps roughly 30–60 bytes in the shipped bundle (most of it is the metadata string itself). The library runtime is ~1.4 KB.

In practice this is rarely visible, because the recommended setup keeps these calls out of production in the first place:

• ESLint blocks them in CI. untodo/no-todo (and no-fixme / no-hack) set to 'error' fails the build. A TODO() that reaches your production bundle is one that escaped review — fix it, don't ship it.
• Runtime is minimal. No throw, no reflection, no I/O — just an optional handler call.
• Server / CLI bundles don't care. A few hundred extra bytes in a Node process is noise.

Zero-overhead opt-out for frontend bundles

If you want to be extra defensive about your shipped bundle, alias untodo to a no-op module in production builds and let the bundler tree-shake the runtime away:

// untodo-noop.ts
export const TODO = (): never => undefined as never;
export const FIXME = TODO;
export const HACK = TODO;
export const defineConfig = <T>(c: T) => c;

// vite.config.ts
import { defineConfig } from 'vite';
import path from 'node:path';

export default defineConfig(({ mode }) => ({
  resolve: {
    alias:
      mode === 'production'
        ? { untodo: path.resolve(__dirname, './untodo-noop.ts') }
        : {},
  },
}));

The same pattern works with Webpack (resolve.alias) and Rollup (@rollup/plugin-alias). Aliasing eliminates the runtime; pair it with terser's pure_funcs: ['TODO', 'FIXME', 'HACK'] if you also want the metadata literals dropped where the call sites allow it.

Scripts

npm run build          # unbuild
npm test               # vitest run
npm run test:coverage  # vitest run --coverage
npm run lint           # eslint .
npm run lint:fix       # eslint . --fix

License

MIT