Network detection in angular or http client proper error

Question

I have two questions.

1. angular httpclient get method returns unknown error when I have lost my internet connection.
2. another question is when I tried navigator.onLine its always returning true. after that I used addeventlistener('online'), addeventlistener('offline') as well as hostlistener also these are not getting trigger hen I lost and found an internet connection.

If I am missing something please let me know