Using environment variables with EAS Update

Learn how to set up and use environment variables with EAS Update.

EAS Build and EAS Update allow setting and getting environment variables at different times. There are multiple steps to ensure the proper environment variables are available when developing, building, and publishing an update.

Setting up the app config

To expose environment variables in a project, you'll have to set up the app config to allow it. After setting it up, you'll be able to access these variables throughout the entire project. As an example, the API_URL is used as an environment variable below. You can use any name for your environment variable.

export default () => ({
  expo: {
    extra: {
      API_URL: process.env.API_URL || null,
    },
    // ...
  },
});

Setting and getting environment variables during development

To set the API_URL environment variable during development, you can prepend the variables before running npx expo start as shown below:

API_URL="http://localhost:3000" expo start

The command above will set the API_URL to "http://localhost:3000". Install the expo-constants library then use the Constants.expoConfig.extra.API_URL property to access it inside a project.

Setting and getting environment variables when building

To set the API_URL environment variable during a build, you can include an "env" property in an eas.json build profile as shown below:

{
  "production": {
    "env": {
      "API_URL": "https://prod.example.com"
    }
  },
  "staging": {
    "env": {
      "API_URL": "https://staging.example.com"
    }
  }
}

When you run the command such as eas build --profile production, the "env" property in the "production" build profile will set the API_URL to https://prod.example.com/ inside the build. Install the expo-constants library then use the Constants.expoConfig.extra.API_URL property to access it inside a project.

Setting and getting environment variables when publishing an update

To set the API_URL environment variable when publishing an update, you can prepend the environment variables before running eas update as shown below:

API_URL="https://prod.example.com" eas update --branch production

When EAS CLI creates the update, it will set the API_URL to https://prod.example.com inside the update's bundle. Install the expo-constants library then use the Constants.expoConfig.extra.API_URL property to access it inside a project.

You can also use the expo-updates library to access API_URL. It is under Updates.manifest?.extra?.expoClient?.extra?.eas?.API_URL. However, Updates.manifest is only present when an update is currently running. If the project is in development, Updates.manifest will be undefined. In addition, if a build is running without an update (for example, it was just downloaded or there are no updates yet), Updates.manifest will also be undefined.

Creating an Env.ts file to get environment variables

Many developers often create a file named Env.ts in their project, which they import into any file that needs to access environment variables. Combining the information above, you can write the following code snippet to access API_URL:

import Constants from 'expo-constants';

function getApiUrl() {
  const API_URL = Constants.expoConfig.extra.API_URL;

  if (!API_URL) {
    throw new Error('API_URL is missing.');
  }

  return API_URL;
}

export const Env = {
  API_URL: getApiUrl(),
};

Using a Babel plugin

Alternatively, you can use a Babel plugin to fill in environment variables. For more information, see using Babel to inline environment variables during build time.