Values returned from BigInt datatypes are returned as JavaScript strings ( https://github.com/pekim/tedious/blob/master/src/tracking-buffer/bigint.coffee), due to JavaScript numbers being limited to 53 bits of data.
Decimal and Numeric types can also expand beyond this range. It would be nice to (optionally) allow sending and receiving numeric data as Strings for Decimal and Numeric types.
For a project I'm working on the id column of the table is a Decimal, so this would be useful.