---

name: typescript-strict description: Enforces strict TypeScript rules and patterns. Use when refactoring code to be type-safe or fixing TS errors.

TypeScript Strict

Enforces strict TypeScript patterns and safety.

Core Principles

• No any: Use unknown or specific types.
• Strict Null Checks: Explicitly handle null and undefined.
• Exhaustive Checks: Use never for exhaustive switch/if-else.
• Type Guards: Use is for custom type guards.
• Branded Types: For critical IDs and values.

Workflows

1. Converting to Strict

• Add "strict": true to tsconfig.json.
• Fix errors service by service.
• Use get_diagnostics to find issues.

2. Fixing any

• Trace the data source.
• Create interfaces/types for external data.
• Use Zod for runtime validation if needed.

Common Patterns

Exhaustive Switch

Copytype Status = 'open' | 'closed';
switch (status) {
  case 'open': ...
  case 'closed': ...
  default:
    const _exhaustiveCheck: never = status;
    return _exhaustiveCheck;
}

Type Guard

Copyfunction isUser(val: unknown): val is User {
  return typeof val === 'object' && val !== null && 'id' in val;
}