Adding web-notification in React app similar to Alert but Not Alert

user story:

We need to alert the user when there a modification or a comment on the thing he has posted by another user.

We are new to react and we are lost in a loop about how to notify the user who is logged in on a different page (maybe his dashboard). The event is performed by another user2 where he is on a page where is commenting on the thing posted by user1.

How can we send an alert to that user1? who currently on a different page saying "there is a new comment on your post".

The issue we are thing about is: The event happens on the comment page. We can send the alert on that comment page. But how will we be able to send a notification to other users on a different page?

I know there is already present. You can take Jiira Board as an example.

Could anyone let us know how can we implement this?