node-pg-types | Type parsing for node-postgres | Parser library

It turns out that through my research jumping from one module to another, that indeed Knex.js does use "node-pg-types" to format the interval columns, and that in turn is using "postgres-interval", neither module document this well at all.

In looking into "postgres-interval" it was evident that the data returned was a JavaScript object which was being encoded into what looked like JSON, however reading the documentation on this module it actually has functions you can call to get the data in any format:

https://github.com/bendrucker/postgres-interval

interval.toPostgres() -> string Returns an interval string. This allows the interval object to be passed into prepared statements.

interval.toISO() -> string Returns an ISO 8601 compliant string.

So the answer is to append .toISO() to your code.

I will notify the developer that this particular behaviour is not well documented so they can look to improve awareness of how Knex.js passes off some of the work to other modules which also pass work off, however I wrote this self answered question so no one else has to spend countless hours trying to figure this out.