Instruction file imported from SafetyMP/Healthcare-Data-Exchange (.github/instructions/typescript.instructions.md). Copyright stays with the author.

TypeScript coding standards (September 2026)

• Write TypeScript, not new application JavaScript. Leave existing tooling .js / .mjs / .cjs files alone.
• Place imports at the top of the module. Do not use inline import() in function bodies except for a documented circular-dependency or optional-runtime case.
• Prefer early returns over nested conditionals.
• On switch over a discriminated union or enum, handle every variant. Use a never check in default so newly added variants fail at compile time.
• Do not introduce any in new production code. Prefer unknown plus narrowing. Do not use non-null assertions to silence strict or noUncheckedIndexedAccess.
• Match this repository's existing formatter and linter. Do not add a second style system.
• Keep public unions narrow. Do not widen a literal union to string without a spec change.
• Do not weaken fail-closed, human-in-the-loop, tenancy, or verify gates to make types compile.

This repository

• web/ is the Next.js clinician console (BFF → gateway :8081). Synthetic FHIR only.
• cd web && npm run verify for the UI gate.