To implement tags in textarea

This is a bit vague question, so I am making a chat application where on typing @ the users of the group pops up, the user has to select from these people., just like WhatsApp.

Now the problem is the user can also do a backspace and delete the 1 character from name. Unlike WhatsApp is the @ is used to tag someone in the group and even a single backspace is made the whole text got deleted.

I am using Angular in the front end

I hope you get the picture of what I am trying to convey, any leads in right direction would be appreciated.