TypeScript adoption hit 78% among professional developers in the 2025 Stack Overflow survey. The language has matured to the point where the ecosystem debates best practices rather than whether to use it. Here's what production teams in 2026 have converged on.
Strict mode is non-negotiable. Enable strictNullChecks, noUncheckedIndexedAccess, exactOptionalPropertyTypes. The incremental cost of fixing strict-mode errors is paid once; the runtime bugs you avoid are ongoing savings. Every major TypeScript-first codebase (Next.js, Prisma, tRPC, SWR) ships with strict: true.
Discriminated unions replace boolean flags and optional fields. Instead of { type: string; userId?: string; error?: string }, use { type: 'success'; userId: string } | { type: 'error'; error: string }. The type narrowing this enables catches mistakes that would otherwise surface at runtime.
The satisfies operator (TypeScript 4.9+) solves the pattern where you want type validation without losing the literal type. const config = { port: 3000, host: 'localhost' } satisfies ServerConfig validates against ServerConfig but keeps 'localhost' as the literal type rather than widening to string.
Avoid enums — use const objects with as const or union literal types instead. TypeScript enums have surprising runtime behavior and don't tree-shake well. 'type Status = 'active' | 'inactive' | 'pending'' is clearer and compiles to nothing.
Use Zod for runtime validation at boundaries (API inputs, environment variables, external data). TypeScript types exist only at compile time; Zod validates at runtime and infers TypeScript types from the schema, giving you both.