Instruction file imported from mattFaber/sveltekit-starter-claude (.github/instructions/typescript.instructions.md). Copyright stays with the author.

TypeScript Standards

Type Rules

• No any — use unknown and narrow with type guards, or define proper interfaces
• No type assertions (as) without a narrowing check immediately before
• All function parameters and return types must be explicit (avoid implicit any from inference gaps)
• Use interface for object shapes that may be extended; type for unions, intersections, primitives

Utility Functions (src/lib/utils/)

• Pure functions only — no Svelte imports, no side effects
• Every exported function must have a co-located *.test.ts with at least one unit test
• Use overloads for functions with multiple call signatures rather than union parameters

Stores (src/lib/stores/)

• Only use stores for global state shared across route boundaries
• Prefer Svelte 5 runes ($state in a .svelte.ts file) for shared reactive state
• Store files must export the store and any derived stores; do not export store internals

// src/lib/stores/user.svelte.ts — preferred for Svelte 5
export const user = $state<User | null>(null);

// src/lib/stores/counter.ts — classic writable (still valid for non-component state)
import { writable } from 'svelte/store';
export const count = writable(0);

Environment Variables

• Private/server secrets: $env/static/private or $env/dynamic/private — import only in *.server.ts files
• Public config: $env/static/public or $env/dynamic/public
• Never pass private env vars to client-visible modules

Response Size

• Return one module/file per response
• For large refactors, make changes function by function, not entire file rewrites