1. In order to deploy to Heroku, I first had to download Heroku Command Line Interface (CLI).

Since I already had an existing Heroku app, I typed the following:

heroku git:remote -a jenlky-shopping-cart
// set git remote heroku to https://git.heroku.com/jenlky-shopping-cart.git

Next I typed git login, it opened a tab and asked me to login. After logging in, I typed git remote --v which returned the following:

heroku  https://git.heroku.com/jenlky-shopping-cart.git (fetch)
heroku  https://git.heroku.com/jenlky-shopping-cart.git (push)
origin  https://github.com/helplah/shopping-cart.git (fetch)
origin  https://github.com/helplah/shopping-cart.git (push)

git push heroku master //push to heroku repo master branch
git push origin master //push to github repo master branch

So basically git add and git commit happen locally, while git remotes are versions of your repository that live on other servers.

You deploy your app by pushing its code to a special Heroku-hosted remote that’s associated with your app.

Lastly, I typed git push heroku master to push it to Heroku server.

2. Localhost is used in development stage. But in Heroku, you cannot use localhost to refer to yourself. I had to conditionally use windows.location.href or href links depending on whether I’m in development in production.

if (process.env.NODE_ENV === 'development') {
window.location.href = 'http://localhost:8080/auth/login';
} else {
window.location.href = 'https://jenlky-shopping-cart.herokuapp.com/auth/login';
}

For example, /auth/login or https://jenlky-shopping-cart.herokuapp.com/cart were used like above.

My corsOption origin was also changed to https://jenlky-shopping-cart.herokuapp.com/ too, instead of http://localhost:3000.