TypeScript Strict Patterns That Prevent Production Bugs

strict: true is the floor

Every Omnetra project ships with strict mode plus noUncheckedIndexedAccess. The latter turns array indexing into T | undefined — annoying for a week, then it eliminates an entire class of undefined-is-not-a-function crashes. Enable both on day one; retrofitting later costs 10x.

Exhaustive switches with never

Route every discriminated union through a switch ending in default: assertNever(x). Adding a union member without handling it becomes a compile error instead of a silent fallthrough. Payment statuses, order states, and role checks all deserve this treatment.

Branded types for IDs

type UserId = string & { readonly brand: unique symbol } stops you passing an OrderId where a UserId belongs — a bug no test suite reliably catches. Add tiny constructor functions (UserId.parse) and the unsafe casts centralize in one auditable place.

Narrow at boundaries

Validate API responses with a schema library and narrow unknown to typed at the edge. Inside the codebase, types stay honest because untrusted data never enters unvalidated. any is banned by lint — unknown plus narrowing is the only path.

Readonly by default

Mark arrays and object properties readonly unless mutation is the point. Half of all state bugs are something mutated from somewhere unexpected; readonly makes the compiler find those somewheres.