Commit hash using React and AWS Amplify

Context:

• A React app in a Git repository.
• AWS Amplify set up to automatically build and deploy your app when changes are made.

Suppose you want to display the hash of the commit where the app was built, perhaps on an about page or in the footer.

How?

Follow these steps:

1. Modify the build script

• Go to the AWS Amplify console.
• Click on "App settings" > "Build settings".
• Under "App build specification", click "Edit".
• Change the build command from npm run build to REACT_APP_COMMIT_ID=$AWS_COMMIT_ID npm run build.

2. Read the value in your app

• Read the value using process.env.REACT_APP_COMMIT_ID, for example: <p>Commit ID: {process.env.REACT_APP_COMMIT_ID}</p>

3. Set up the value in development

• Add a file in the root of the project called .env.development.
• Add a development version of the variable, e.g. REACT_APP_COMMIT_ID=abcdef.

Why?

In the above, REACT_APP_COMMIT_ID is the name of an environment variable to be used at build time (more details). It's important that its name starts with REACT_APP, as otherwise React won't be able to see its value (this is a security feature to avoid accidentally exposing secrets).

In part 1, we set its value to $AWS_COMMIT_ID. This is a reference to an Amplify build-time environment variable containing the hash of the commit being built. There are a number of environment variables automatically set by Amplify (see here), and you can even set your own (see here).