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Better switches with Zod and TypeScript

Riley Tomasek

Zod discriminated unions allow a switch case to perform automated type narrowing and cause a TypeScript error if a case is missed.

// This adds type narrowing by the intent property
const Schema = z.discriminatedUnion('intent', [
  z.object({ intent: z.literal('delete'), id: z.string() }),
  z.object({ intent: z.literal('create'), name: z.string() }),
]);

const data = Schema.parse({ intent: 'delete', id: '123' });

switch (data.intent) {
  case 'delete':
    // data is now narrowed to { intent: 'delete', id: string }
    return;
  case 'create':
    // data is now narrowed to { intent: 'create', name: string }
    return;
  default:
    // data is now narrowed to never. This will error if a case is missing.
    const _exhaustiveCheck: never = data;
}