Download the example or clone the repo:
curl https://codeload.github.com/zeit/next.js/tar.gz/master | tar -xz --strip=2 next.js-master/examples/with-dotenv
cd with-dotenvInstall it and run:
npm install
npm run devDeploy it to the cloud with now (download)
nowThis example shows the most basic idea of babel replacement from multiple environment. We have 1 env variable: TEST which will be replaced in development env and in production env with different babel plugin. In local development, babel reads .env file and replace process.env.* in your nextjs files. In production env (such as heroku), babel reads the ENV and replace process.env.* in your nextjs files. Thus no more needed to commit your secrets anymore.
Of course, please put .env* in your .gitignore when using this example locally.
If for some reason the variable is not displayed on the page, try clearing the babel-loader cache:
rm -rf ./node_modules/.cache/babel-loader