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TypeScript best practices. Use when reading or editing any .ts or .tsx file.
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| name | typescript-best-practices |
| description | TypeScript best practices. Use when reading or editing any .ts or .tsx file. |
Apply the type-system-discipline principle skill first; this skill grounds it in TypeScript syntax.
| Rule | Summary |
|---|---|
| Discriminated unions | Model variants with a kind literal discriminant so impossible states can't be represented. No optional-field bags. |
| Branded types | Brand primitives with & { readonly __brand: "X" } so they can't be mixed up. Validate once at creation. |
unknown over any | External data is unknown. any disables type checking everywhere it touches. |
No as casts | Every as is a runtime crash waiting. Cast only after validation. |
| Narrowing hierarchy | Discriminant switch > in operator > typeof/instanceof > user-defined type guard > as. |
| Type guards | Must verify the claim. A lying guard is worse than as because the bug hides behind a name that says it's safe. Name them isX or hasX. |
| Exhaustiveness | Inline const _exhaustive: never = x; in default arms so the compiler errors when a new variant is added. |
satisfies over as | Validates the value without widening literal types. |
| Boundary validation | Validate where data crosses in; trust types inside. See the boundary-discipline principle skill. |
| Schema-derived types | Reach for Pick/Omit/Parameters/ReturnType/Awaited/typeof before declaring a new interface. |
| Object args | Pass objects, not positional, so argument order is self-documenting. Skip on hot paths (per-frame render, tokenizers, parsers). |
Examples: references/patterns.md.
Reproduce triaged Slack bugs through a configured app-control adapter, verify existing fixes, and open a bounded draft pull request only after before-and-after proof. Use only from the configured Benny repro automation.
Configure Benny and prepare its triage and repro automations. Use when installing Benny or changing its Slack, tracker, repository, routing, control, model, or budget settings.
Triage Slack issue reports with one thread-only verdict, evidence review, cause-aware routing, tracker dedupe, and fail-closed ticket creation. Use only from the configured Benny triage automation.
Find what a change could break somewhere else before it ships, beyond the diff, and prove the one fact it's safe because of by running real code instead of writing it up. Use for 'blast radius of X', 'what could this break', or reviewing a small diff you don't trust.
Reconstruct your recent working context from your own chat history, live state, and the shared record (user reports, prior fixes, incidents), then hand back a tight current-state brief. Use for 'recall my work on X', 'catch me up', 'what have I been working on', 'where did I leave off', before starting or resuming work.
poteto's agent style for concise, detailed responses, deliberate subagents, unslopped prose, simple code, and verified work. Use for poteto, /poteto-mode, or requests to work in this style.
