How to Use Environment Variables with Create-React-App

Oct 28, 2019

Environment Variables are a critical tool in getting your app set up correctly, but can be tricky for beginners. Create React App also has a couple other nuances to be aware of.

For background, environment variables are how we wire things up to behave differently between different environments (i.e. development vs production). For instance, you often need your dev environment to point to a different API, or for your payments library to only charge money in production, etc.

Setting Values

If you’re using Create-React-App, you can add your own custom environment variables.

create a file called .env in the root directory of your project
add a new line in the file for each variable you need, making sure to prefix the variable name with REACT_APP_. For instance:

REACT_APP_API_URL=http://api.example.com

🚨 Don’t miss this! The variable name must start with REACT_APP_ otherwise it won’t work.

Restart the dev server.

Reading Values

Environment variable values can be read using process.env.REACT_APP_VARIABLE_NAME, like so:

render() {
  return (
    <div>
      Current API url: {process.env.REACT_APP_API_URL}.
    </div>
  )
}

A few more things…

Client side .env values are not secret. They can be found by anyone who wants to sift through your site’s JavaScript code.
.env files should be committed and tracked in version control with the rest of your project.
You may want some environment variables that are only for you specifically (not necessarily others on your team) that you don’t want to be tracked via version control. For these, you can create another file in the project root, called .env.local. Variables placed here will override the .env value if both are present. This file should not be committed or tracked in version control.
Changes to .env files don’t take effect until you restart the server.
To comment out a line in a .env file, prefix it with a “#” character, like so:

# REACT_APP_API_URL=http://api.example.com
REACT_APP_API_URL=http://api2.example.com

Create-React-App comes with one default environment variable out-of-the-box: NODE_ENV. This will be set to “development”, “test”, or “production” depending on your current environment. It can be read from process.env.NODE_ENV.

For more details, check the official Create React App docs.

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