Using Web Firebase SDK in Expo Snack

Evan Bacon

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Exposition

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1 min read

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Aug 13, 2018

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TL;DR: if (!firebase.apps.length) firebase.initializeApp({ … }); instead of firebase.initializeApp({ … });

If you have tried using Firebase in a snack.expo.io you may have noticed that the hot reloading will cause it to throw errors and not function properly.

Device: (78:20) Firebase: Firebase App named '[DEFAULT]' already exists (app/duplicate-app).
  Evaluating module://Firebase/Fire.js
  Evaluating module://Screens/Login.js
  Evaluating module://AuthStateLayer.js
  Evaluating module://App.js
  Loading module://App.js

Fixing this is very simple. Just check to make sure the app hasn’t been initialized before calling firebase.initializeApp({ ... });

You can do that like this:

if (!firebase.apps.length) firebase.initializeApp({ ... });

It’s kinda upsetting that firebase doesn’t just throw a warning and tell you what to do. 🙃

Thanks for reading

Hope this helps — Tweet at me any questions, Medium comments are hard to reply to 😕