Code in Bits and Pieces

Expo Updates · Custom update notification

June 15, 2021 • ☕️ 6 min read

As you might now, I am a big Expo fan. Various of my project are built on top of this marvelous framework and help me develop, build, deploy, and quickly iterate on iOS, Android, and web apps from the same TypeScript code bases.

In this article I’d like to show you how I use expo-updates to show a custom update ready notification instead of relying on the start-up sequence, or the user periodically closing the application.

The Updates API from expo allows you to programmatically control and respond to over-the-air updates to your app.

Typewriter with a paper sticking out with a single word: "Update"

Configuration

Make sure your app.json has the following:

{
  "updates": {
    "enabled": true,
    "fallbackToCacheTimeout": 0,
    "checkAutomatically": "ON_ERROR_RECOVERY"
  }
}

This will prevent expo from checking for updates at all, unless you run into a fatal JS error. In general this means that expo will only check for updates when it’s not confident the user will be able to get to the in-app updater.

However, your start-up sequence might also crash, and since it will use the build from cache, that’s unlikely to resolve itself. If you’re not confident that the updates you’ll push are crash-free-on-load, use:

{
  "updates": {
    "enabled": true,
    "fallbackToCacheTimeout": 15000,
    "checkAutomatically": "ON_ERROR_RECOVERY"
  }
}

Mounting the updater

Because the expo-updates API is (currently) not available on web, I recommend to conditionally load the OtaUpdater, which I’ll show you how to write in a minute.

import { Platform } from 'react-native';

// Your application might look differently. What's important is that you mount
// the component at the top-level, and that it stays mounted throughout the
// lifecycle of the application.
export default function App() {
  return (
    <SafeAreaProvider>
      <Root />
      {/* insert here */}      <StatusBar />
    </SafeAreaProvider>
  )
}

Since you want to exclude web, insert the following:

{Platform.OS !== 'web' && <OtaUpdater />}

Creating OtaUpdater

Here’s the idea:

  • Periodically check for updates using Updates.checkForUpdateAsync()
  • When there is one, download it using Updates.fetchUpdateAsync()
  • When that has finished, show some UI that calls Updates.reloadAsync()

Let’s start with the code that would check for updates:

import * as Updates from 'expo-updates';

async function checkForUpdates(): Promise<true> {
  const update = await Updates.checkForUpdateAsync()
  if (!value.isAvailable) {
    throw new Error('No updates available')
  }

  const result = await Updates.fetchUpdateAsync()
  if (!result.isNew) {
    throw new Error('Fetched update is not new')
  }

  return true
}

There are two steps.

    1. Check if a new update is available
    1. Download it and assert that it’s newer than what’s available

Next I want to run this code only after a certain amount of time has passed.

In this case I’ll use react-native-use-timestamp, a package that allows you to re-render a component on an interval without setting long running timers and without keeping the app alive, and defer when animations are running. It also allows you to test it because it relies on use-timestamp which comes with “mocking” out-of-the-box.

import { useInaccurateTimestamp } from 'react-native-use-timestamp';

// How often do we want to render?
const INTERVAL_RENDER = 1000 * (__DEV__ ? 10 : 60)

export function OtaUpdater() {
  const now = useInaccurateTimestamp({ every: INTERVAL_RENDER });
  const isMounted = useRef(true)
  const [updateIsAvailable, setUpdateAvailable] = useState(false);

  useEffect(() => {
    isMounted.current = true

    return () => {
      isMounted.current = false
    }
  }, [])

  useEffect(() => {
    if (updateIsAvailable) {
      return
    }

    checkForUpdates()
      .then(() => { isMounted.current && setUpdateAvailable(true) })
      .catch((_reason) => { /* you can inspect _reason */ })
  }, [now])

  return null
}

This works pretty well. Every 60 seconds, it will check for an update and when it’s ready, it sets updateIsAvailable to true. However, it’s not very nice for your user!

  • Checking the internet potentially means reconnecting to the internet which is energy consuming
  • We don’t need to tell the user every minute that an update is ready

Let’s add a 15 minute interval. You might be tempted to increase INTERVAL_RENDER to 15 minutes, but that would be a mistake if you’re trying to avoid long running timers.

💡 Note: long running timers aren’t bad, even though there is a warning message. It mostly means that the timer is no longer accurate if the user suspends the application. In our case, that’s not a problem but we do care about the 15 minute interval. What we don’t want is that the user must be active for 15 minutes before we check.

Instead, here is a way to accomplish that:

// How often should it actually check for an update?const INTERVAL_OTA_CHECK = 1000 * 60 * 15
export function OtaUpdater() {
  // ... the old code

  // Setting this to initially zero means there will _always_ be a check on  // mount, which is nice, because that means a check when the app starts.  const [lastUpdate, setLastUpdate] = useState(0)
  useEffect(() => {
    if (now - lastUpdate < INTERVAL_OTA_CHECK) {      return    }    setLastUpdate(now)
    // ... the old code

  }, [now])

  return null
}

Each time the effect runs because of the timestamp that has changed, it will check how long it has been since the last real check.

Everything together:

import { useInaccurateTimestamp } from 'react-native-use-timestamp';

// How often do we want to render?
const INTERVAL_RENDER = 1000 * (__DEV__ ? 10 : 60)

// How often should it actually check for an update?
const INTERVAL_OTA_CHECK = 1000 * 60 * 15

export function OtaUpdater() {
  const now = useInaccurateTimestamp({ every: INTERVAL_RENDER });
  const isMounted = useRef(true)
  const [updateIsAvailable, setUpdateAvailable] = useState(false);

  // Setting this to initially zero means there will _always_ be a check on
  // mount, which is nice, because that means a check when the app starts.
  const lastUpdate = useRef(0)

  useEffect(() => {
    isMounted.current = true

    return () => {
      isMounted.current = false
    }
  }, [])

  useEffect(() => {
    if (updateIsAvailable) {
      return
    }

    if (now - lastUpdate.current < INTERVAL_OTA_CHECK) {
      return
    }

    lastUpdate.current = now

    checkForUpdates()
      .then(() => { isMounted.current && setUpdateAvailable(true) })
      .catch((_reason) => { /* you can inspect _reason */ })
  }, [now])

  return null
}

All that’s left for you to do is replace null with your UI. Don’t forget to call Updates.reloadAsync() on some action / button. I often use a Snackbar as provided by react-native-paper which looks something like this:

return (
  <Portal>
    <Snackbar
      visible={updateIsAvailable}
      onDismiss={() => {}}
      action={{
        label: 'Apply update',
        onPress: () => { Updates.reloadAsync() },
      }}>
      Hey there! We got an update for you 🥳🎉.
    </Snackbar>
  </Portal>
)

Bonus: showing an update-specific message

Because you have access to the new Manifest, you can use it to show a custom message.

async function checkForUpdates(): Promise<string> {  const update = await Updates.checkForUpdateAsync()
  if (!value.isAvailable) {
    throw new Error('No updates available')
  }

  const result = await Updates.fetchUpdateAsync()
  if (!result.isNew) {
    throw new Error('Fetched update is not new')
  }

  // Using the "extra": { "update-message": "..." } from app.json  return result.manifest.extra['update-message']}

You can also build a message out of the new version, or, optionally fetch the changelog from a service you provide.

Have fun!