next.js/examples/with-universal-configuration-build-time/README.md

With universal configuration

How to use

Using create-next-app

Execute create-next-app with Yarn or npx to bootstrap the example:

npx create-next-app --example with-universal-configuration-build-time with-universal-configuration-build-time-app
# or
yarn create next-app --example with-universal-configuration-build-time with-universal-configuration-build-time-app

Download manually

Download the example:

curl https://codeload.github.com/zeit/next.js/tar.gz/canary | tar -xz --strip=2 next.js-canary/examples/with-universal-configuration-build-time
cd with-universal-configuration-build-time

Install it and run:

npm install
VARIABLE_EXAMPLE=next.js npm run dev
# or
yarn
VARIABLE_EXAMPLE=next.js yarn dev

Deploy it to the cloud with now (download)

now

The idea behind the example

This example shows how to use environment variables and customize one based on NODE_ENV for your application using dotenv, a .env-file and next.config.js.

When you build your application the environment variable is transformed into a primitive (string or undefined) and can only be changed with a new build. This happens for both client-side and server-side. If the environment variable is used directly in your application it will only have an effect on the server side, not the client side.

Please note

• It is a bad practice to commit env vars to a repository. Thats why you should normally gitignore your .env file.
• Any env var you expose in next.config.js will be publicly available and exposed to the client.
• This example sets the environment configuration at build time, meaning the same build might not be used in e.g. both staging and production. For a solution which sets the environment at runtime, see the example with-universal-configuration-runtime.
• If you have many variables in .env and want to expose them without listing them all in next.config.js, see the example with-dotenv. That example automatically exposes any variable that has been referenced in code, but keeps all other variables secret.