Correct setting of environment variables when building SPA?

Question

React

Is it necessary to specify environment variables in a script command?
for example
package.json:
"build" : "API_URL=api/ node app.js"
And in the build:
npm run build
or can you specify when building a teamcity like this?
package.json:
"build" : "node app.js"
And in assembly:

ENV API_URL=api/
npm run build

Will the variables be available? Now for some reason they are undefined

Answer 1

environment variables in create react app must start with REACT_APP_,
then they will be pulled into the project when building.
https://create-react-app.dev/docs/adding-custom-en...