Removing keys/values from a JSONB object in Postgresql - postgresql

Question

I am trying to adapt the Audit trigger to use JSONB instead of hstore. This function stores all inserts/updates/deletes in a separate table.
The trigger has 2 interesting fields : row_data (contains the OLD.* values) and changed_fields (contains only the modified fields/values).
I have trouble converting this part.
In the original function, we have the following code :
audit_row.row_data = hstore(OLD.*);
audit_row.changed_fields = (hstore(NEW.*) - audit_row.row_data);
In my implementation, row_data and changed_fields are of type JSONB
In the documentation, the "-" operator will match on keys only and I obviously need to match on both key AND value.
As an example, if the OLD value is this :
select jsonb_object('{field1,1,field2,a string,field3,TRUE}');
jsonb_object
---------------------------------------------------------
{"field1": "1", "field2": "a string", "field3": "TRUE"}
and only field2 was updated, I need to see this :
?column?
------------------------
{"field2": "a string"}
which I would get with this query :
select jsonb_object('{field1,1,field2,a string,field3,TRUE}')
#- '{field1}'
#- '{field3}';
Is there an elegant way to do this (like how it's done with hstore) or should I keep the hstore implementation and convert changed_fields to JSONB (with everything seen as text) ?
I could also loop on all fields in NEW and add them to changed_fields if a match could not be found but how to do this inside a function ?