I'm curious but why is the node version so low to not allow URLSearchParams iterating over that, splitting, and then reconstructing recersivly is still a good kata. Why teach 20 year old code practises?

This can maybe offer some flow contrl and string concatination practise but with that the solution is quite simplistic compared to a more traditional flow control kata like fizz-buzz. However, this kata does provide an oppertunity to practice internationalization APIs like handling lists formatting and number formatting. Unfortunatly, the tests don't exercise that and the blueprint code ignores I18N libs. The string building centric focus of the requirements force the use of the en-GB (2023) locale. It also losses out on practicing writing ICU Message Syntax which is a popular and often used syntax for many I18N libraries and translation services.