Feature Request: json_extend, jsonb_extend

It would be nice if PostgreSQL has *_extend (similar to $.extend from jQuery or _.extend from UnderscoreJs) for JSON/JSONB columns, so we could write it like this:

UPDATE tablename 

  SET jsoncolumn = json_extend(jsoncolumn, $2) 

  WHERE id = $1;

instead of this:

UPDATE tablename 

  SET data = (

    SELECT json_object_agg(key, value)::jsonb 

      FROM 

        ( SELECT * FROM jsonb_each( SELECT data FROM tablename WHERE id=$1 )

          UNION ALL

          SELECT * FROM jsonb_each( $2 ) 

        ) x1

  ) WHERE id=$1;