0.2.6 • Public • Published


A runtime environment handler for React.js apps that have been bootstraped using create-react-app.


The runtime-env-cra package was meant to be used in Docker or VM based environments, where you have full control over how your application will start. Sadly, runtime-env-cra can not be used if you are using S3 or another static file serving solution.

  • Supported node.js versions due to yargs is 12 or greater

  • Installation

$ npm install runtime-env-cra
  • Add the following to public/index.html inside the <head> tag:
<!-- Runtime environment variables -->
<script src="%PUBLIC_URL%/runtime-env.js"></script>
  • Modify your start script to the following in your package.json:
"scripts": {
  "start": "NODE_ENV=development runtime-env-cra --config-name=./public/runtime-env.js && react-scripts start",
  • If you are on windows, you need to use cross-env
"scripts": {
  "start": "cross-env NODE_ENV=development runtime-env-cra --config-name=./public/runtime-env.js && react-scripts start",

The script parses everything based on your .env file and adds it to window.__RUNTIME_CONFIG__. If you pass NODE_ENV=development for the script, it will use the values from your .env, but if you provide anything else than development or nothing for NODE_ENV it will parse environment variables from process.env. This way you can dynamically set your environment variables in production/staging environments without the need to rebuild your project.


This script uses your .env file by default to parse the environment variables to window.__RUNTIME_CONFIG__, so be sure to have one in your project! After modifying the start script and public/index.html described in the section above, you should be good to go!

CLI options

  • Display the help section.
$ runtime-env-cra --help | -h
  • Relative path and file name that will be generated. Default is ./runtime-env.js
$ runtime-env-cra --config-name | -cn
  • Relative path and name of your env file. Default is ./.env
$ runtime-env-cra --env-file | -ef

Typescript usage

  • Create ./src/types/globals.ts file and pase the following (modify the __RUNTIME_CONFIG__ properties to match your environment):
export {};

declare global {
  interface Window {
      API_URL: string;
      NODE_ENV: string;
  • Add "include": ["src/types"] to your tsconfig.json.
  "compilerOptions": { ... },
  "include": ["src/types"]

Usage in Docker

You must have an example of your env layout. A project usually have a .env.example which represents that and will not contain any sensitive information. Inside a docker container we can lean on the .env.example. Make sure your .env.example is always up to date!

  • Using in an alpine based container
# copy .env.example as .env to the container
COPY .env.example .env

# install nodejs & npm
RUN apk add --update nodejs
RUN apk add --update npm

# install runtime-env-cra package
RUN npm i -g runtime-env-cra

# start the app with the following CMD
CMD ["/bin/sh", "-c", "runtime-env-cra && nginx -g \"daemon off;\""]


  • Create react app with typescript template, including Dockerfile and docker-compose. (source)
  • Create react app without typescript, including Dockerfile and docker-compose. (source)

Test coverage

File               | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
All files          |     100 |      100 |     100 |     100 |
 generateConfig.js |     100 |      100 |     100 |     100 |
 utils.js          |     100 |      100 |     100 |     100 |
Test Suites: 1 passed, 1 total
Tests:       5 passed, 5 total
Snapshots:   0 total
Time:        1.751 s





If you find a bug or have a question about the usage, feel free to open an issue!

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npm i @hyperting/runtime-env-cra

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  • marconalon