The issue with process.env variable being empty in browser is because browser doesn’t have real access to the process of the node.js. It’s run inside the browser though.

Usage of process.env.ANYTHING is usually achieved by plugins like https://webpack.js.org/plugins/define-plugin/ which just simply replace any occurrence of process.env.ANYTINHG with env variable during BUILD time. It really does just simple str.replace(/process.env.ANYTING/value/) this needs to be done during build time as once you output dist bundle.js you don’t have access to the ENV variables.

Replacing during build time

Therefore you need to be sure that when you are producing production build e.g with yarn build you are using webpack.DefinePlugin and replacing those process.env calls with current ENV values. They can’t be injected in runtime.

Injecting in runtime

When you need to access env variables in runtime it’s basically impossible in JavaScript in browser. There are some sort of hacks for example for NGINX which can serialize current env variables to the window.ENV variable and in your app you will not use process.env but window.ENV. So you need to either have ENV variables available while you are building the application or build mechanism which will dynamically output current ENV as json to window and access with react. If you are using docker it can be done with ENTRYPOINT otherwise you need some bash script which will always output current ENV variables as JSON to the index.html of your app