typescript-best-practices

Type external data as unknown instead of any, since any disables type checking everywhere it touches. Narrow unknown with typeof, instanceof, or the in operator before accessing properties, so the compiler verifies each access.

Give every variant a shared literal discriminant field like kind with a unique value per variant, for example { kind: "loading" } or { kind: "ready"; diff: GitDiff }. This makes contradictory states unrepresentable, unlike boolean flags plus optional fields.

Use satisfies when you want to validate a value against a type while preserving its literal types, such as { theme: "dark" } satisfies Config. Use as only after runtime validation has verified the claim, since every as is a potential runtime crash.

Yes, model a non-empty array as a variadic tuple: type NonEmpty<T> = [T, ...T[]]. Narrow a plain array once with a guard like arr.length > 0, and the non-empty fact then travels in the type without repeated checks.

Without an exhaustiveness check, adding a variant to a union does not error in existing switches. Add const _exhaustive: never = x; in the default arm so the compiler errors when a new variant is unhandled.

Object arguments are preferred for self-documenting, order-independent calls, but skip them on hot paths. Per-frame rendering, tokenizers, and parsers in tight loops should avoid the allocation cost of creating argument objects.