File-based navigation with expo-router

Native apps have no URL bar, but expo-router gives you file-based routing anyway: every file in app/ becomes a screen, and the directory structure becomes the navigation tree. If you've used the Next.js App Router, this is the same idea with native transitions instead of page loads.

app/
  _layout.tsx        → root navigator (a Stack)
  index.tsx          → "/"
  settings.tsx       → "/settings"
  users/
    [id].tsx         → "/users/42"  (dynamic segment)

A _layout.tsx file wraps every route in its directory with a navigator. The two you'll use constantly are Stack (screens slide on top of each other, back gesture included) and Tabs (a bottom tab bar):

// app/_layout.tsx — every screen renders inside this Stack
import { Stack } from "expo-router";

export default function RootLayout() {
  return <Stack screenOptions={{ headerShown: true }} />;
}

Navigation is declarative with <Link>, or imperative with the router object. Dynamic segments arrive through a hook:

// app/index.tsx
import { Link } from "expo-router";
import { Text } from "react-native";

export default function Home() {
  return <Link href="/users/42"><Text>Open user 42</Text></Link>;
}

// app/users/[id].tsx
import { useLocalSearchParams } from "expo-router";
import { Text } from "react-native";

export default function User() {
  const { id } = useLocalSearchParams<{ id: string }>();
  return <Text>User {id}</Text>;
}

Route groups

Parenthesized directories like (tabs) or (auth) group routes without adding a URL segment. The classic pattern: the root Stack contains a (tabs) group holding the tab navigator, plus modal screens that push over the tabs. (auth) holds login screens you conditionally redirect into. app/(tabs)/index.tsx is still just /.

The challenge is a JS model of the router's core trick: matching a path against file-derived route patterns, extracting [bracket] params, and ignoring group segments.

Next: past the JS sandbox — cameras, notifications, and the permissions dance that guards them.