# Typescript

> TypeScript coding standards — apply when writing, reviewing, or refactoring .ts/.tsx, or naming/renaming .ts files (camelCase casing).

- Skill: `forcedotcom/typescript` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add forcedotcom/typescript`
- Raw SKILL.md: https://api.skillmd.com/api/skills/forcedotcom/typescript/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: forcedotcom (https://skillmd.com/u/forcedotcom)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/forcedotcom/typescript

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- no barrel files
- no `void` for async - use async/effect (exception [vscode-window-messages](../vscode-window-messages/SKILL.md))
- no `export *` - name exports explicitly
- prefer `undefined` over null (unless server requires null)
- prefer `undefined` over empty string
- prefer map/filter over loops/conditionals
- avoid mutation
- avoid `any`
- derive types from the source of truth; don't hand-write or narrow them to satisfy the compiler.  ex: use ReturnType<> to match something
- no enums or namespaces (enums compile to weird JS; use string union types instead; exception: interfaces defined outside this repo that we can't change)
- no runtime errors for developer mistakes (use types to ensure exhaustive switch/case; don't throw for null/undefined when input/consumer is within our control)
- .ts filenames: camelCase, no hyphens, no leading capitals
- preserve comments when refactoring; remove/fix if wrong/obsolete
- exported functions: single-line jsdoc /\*_ foo _/ if name unclear; no params/return (TS provides types)
- look for uses of (Object|Map).groupBy instead of older patterns
- redundant empty-collection guards: if `arr.find/some/every/map/filter/reduce` already returns the same value for an empty array, drop the `if (arr.length === 0) return …` guard. e.g. `find` on `[]` is `undefined`, so guarding `return undefined` is dead code.
- no needless const declarations: return directly instead of `const x = val; return x` (exception: complex expressions where const improves readability)