Dynamic runtime environment variables for static sites and SPAs (e.g. Create React App)

A quick tip on how you can make your SPA (e.g. a Create-React-App app) or static site's environment variables configurable at runtime — not compile time.

[iKlalter]

This is exactly what I was looking for and explained very clearly. Thanks a lot!

[nikitaalekseev]

Thank you!
This is great explanation and trick!
But wouldn't this be unsafe due window object is available from DevTools console?
Can we pass some secret keys this way?

[dalthonmh]

How could I pass an env like where is the backend url service