typescript-best-practices

# TypeScript Best Practices ## When to Use Use this skill when: - Writing new TypeScript code - Reviewing TypeScript pull requests - Refactoring JavaScript to TypeScript ## Triggers Activated when editing `.ts` or `.tsx` files in the project. ## Rules ### Always - Always use `const` for variables that won't be reassigned - Always use explicit return types on exported functions - Always prefer `interface` over `type` for object shapes ### Never - Never use `any` — use `unknown` instead - Never use `var` — use `const` or `let` - Never ignore TypeScript errors with `@ts-ignore` ## Examples ```typescript // Good: explicit return type export function calculateTotal(items: Item[]): number { return items.reduce((sum, item) => sum + item.price, 0); } ``` ```typescript // Good: discriminated union type Result<T> = | { success: true; data: T } | { success: false; error: Error }; ``` ## Boundaries - Do not modify `tsconfig.json` without explicit permission - Do not add new dependencies without checking existing utilities - Focus only on TypeScript patterns, not runtime behavior