Device APIs: Camera, Location, and Permissions

One of Expo's biggest advantages is instant access to native device features through simple JavaScript APIs, no native code required. Nearly all of them follow the same permission pattern.

The permission pattern

import * as Location from 'expo-location';

async function getCurrentLocation() {
  const { status } = await Location.requestForegroundPermissionsAsync();
  if (status !== 'granted') {
    console.log('Permission denied');
    return null;
  }
  const location = await Location.getCurrentPositionAsync({});
  return location.coords;
}

Every device API works the same way: request permission (the OS shows a native prompt the first time), check the result, then use the API only if granted. Never assume permission, always request and check.

Using the camera

import { CameraView, useCameraPermissions } from 'expo-camera';

function ScannerScreen() {
  const [permission, requestPermission] = useCameraPermissions();

  if (!permission) return null; // still loading
  if (!permission.granted) {
    return <Button title="Grant camera access" onPress={requestPermission} />;
  }

  return <CameraView style={{ flex: 1 }} />;
}

useCameraPermissions() is a hook version of the same request/check pattern, common for APIs used directly inside a component.

Declaring permissions in app.json

Some permissions (especially on iOS) also need a usage description declared in app.json, explaining why your app wants access, shown to the user in the native permission dialog:

{
  "expo": {
    "ios": {
      "infoPlist": {
        "NSCameraUsageDescription": "This app uses the camera to scan QR codes."
      }
    }
  }
}