How to delete a word when removing a letter from it?

Question

JavaScript

Good day to all. There is an input in which the user can enter text \ edit it, etc ... The
input searches the site.
Example
Vasya OR Kolya AND NOT Petrov.
In case of deleting a letter from any place for Vasya \ Kolya \ Petrov - standard behavior.
If I remove a letter anywhere from OR / AND NOT / etc then the whole word needs to be removed.
test change event. There is an old and a new meaning.
How to compare them correctly and determine what the difference is in this place, and remove the desired design?