Environment-specific configurations are an important part of most
applications. You can access environment variables in your create-react-app
code using process.env.
There are a couple built-in environment variables, such as NODE_ENV.
Anything custom that you want to provide must be prepended with
REACT_APP_. If it isn't, that environment variable will be ignored with no
warning.
The following line of code
const base_api_url = process.env.REACT_APP_BASE_API_URL;will have access to whatever that value is in the environment when the server is started or the app is built.
Set that value inline like so:
REACT_APP_BASE_API_URL="https://api.my_app.com" yarn start