Functions, Async Flows, and Typed Errors

Design function contracts for services, handlers, callbacks, and async workflows.

36 min

3 sections

functions

async

result

errors

01. Function Contracts

Section 1 of 3

Function types should describe what the caller must provide and what the function guarantees. In enterprise code, clear function boundaries are more valuable than clever inference because they communicate ownership between modules.

typescript

type AuditWriter = (event: {
  actorId: string;
  action: string;
  resourceId: string;
  metadata?: Record<string, string>;
}) => Promise<void>;

async function closeTicket(
  ticketId: string,
  actorId: string,
  writeAudit: AuditWriter
): Promise<void> {
  await writeAudit({
    actorId,
    action: "ticket.close",
    resourceId: ticketId,
  });
}

Narrowing and Runtime Boundaries

Runtime Validation and Schema Boundaries

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