Runtime env var support for static javascript apps on Heroku
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Heroku JS Runtime Env

Use runtime environment variables in bundled/minified javascript apps.

Build Status npm Module


Designed for create-react-app-buildpack. See its documentation to use this module for Runtime configuration.

See also 🔬🚧 experimental, generalized usage with heroku-js-runtime-env-buildpack.


Normally javascript apps are compiled into a bundle before being deployed. During this build phase, environment variables may be embedded in the javascript bundle, such as with Webpack DefinePlugin.

When hosting on a 12-factor platform like Heroku, these embedded values may go stale when setting new config vars or promoting through a pipeline.

How Does It Work?

When developing your app, use Runtime environment variables from create-react-app-buildpack.

Then, each time the app starts-up on Heroku, a .profile.d script (installed from the buildpack) is executed which fills in a JSON placeholder in the JavaScript bundle with the runtime environment variables. The result is 🍃fresh runtime environment variables in the production javascript bundle without recompiling.