Adding host name for calling functions from front-end
Go to functions in Firebase and copy host name from function url.
Then, paste it into to hostname const:
Paste to value of hostName
Deploy cloud functions
At first, let's setup firebase CLI as mentioned in official docs:
$ npm install -g firebase-tools
You'll need a Node.js environment to write functions, and you'll need the Firebase CLI to deploy functions to the Cloud Functions runtime. For installing Node.js and npm, Node Version Manager is recommended.