expo-router + exactOptionalPropertyTypes

Minimal reproduction showing that expo-router@55.0.3 types are incompatible with TypeScript's exactOptionalPropertyTypes.

Reproduce

Open in StackBlitz (run npx tsc --noEmit in the terminal)

Or locally:

git clone https://github.com/YevheniiKotyrlo/str-expo-router-eopt.git
cd str-expo-router-eopt
npm install
npx tsc --noEmit

Expected: 0 errors Actual: 3 errors (TS2375, TS2345) in consumer code — even with skipLibCheck: true

repro.tsx(19,7): error TS2375: Type '{ name: string; options: ... | undefined; }' is not assignable
  to type 'ScreenProps' with 'exactOptionalPropertyTypes: true'.
repro.tsx(32,3): error TS2375: Type '{ name: string; redirect: undefined; ... }' is not assignable
  to type 'Partial<ScreenProps>' with 'exactOptionalPropertyTypes: true'.
repro.tsx(48,15): error TS2345: Argument of type '{ pathname: string; params: undefined; }' is not
  assignable to parameter of type 'string | HrefObject'.

With skipLibCheck: false

npx tsc --noEmit --skipLibCheck false

144 errors across expo-router, @react-navigation, and react-native .d.ts files.

Without the flag (baseline)

npx tsc --noEmit --exactOptionalPropertyTypes false

0 errors — confirms exactOptionalPropertyTypes is the sole cause.

What's happening

With exactOptionalPropertyTypes, prop?: T means "if present, must be exactly T" — explicitly passing undefined is a type error. The fix is prop?: T | undefined.

expo-router's exported types (ScreenProps, HrefObject, etc.) define optional properties as prop?: T without | undefined. Consumer code that assigns undefined to these properties — a common pattern for conditional options — gets type errors.

skipLibCheck: true doesn't help because the errors are in the consumer's .tsx files, not in .d.ts files. TypeScript still loads and enforces the types from .d.ts declarations.

Why this matters now

• TypeScript 5.9's tsc --init enables exactOptionalPropertyProperties by default
• Libraries commonly used with Expo have already shipped support: Zustand, TanStack Query, Zod v4, Storybook
• react-navigation has PRs in review adding the same support

Fix

Add | undefined to optional properties in expo-router's type definitions. This is backwards-compatible: prop?: T and prop?: T | undefined are identical when exactOptionalPropertyTypes is disabled.

See expo/expo#43506.

Environment

• expo: 55.0.3
• expo-router: 55.0.3
• react-native: 0.83.2
• react: 19.2.0
• typescript: 5.9.3
• expo-doctor: 17/17 checks passed