Node.js makes it easy to start a server and hard to keep one organised. A few routes become a few dozen, shared logic drifts into copy pasted handlers, and six months later nobody is sure where a feature lives. NestJS is a framework that gives a Node backend a deliberate shape from the first file, borrowing ideas from Angular and from enterprise frameworks in other languages.

The shape has three parts, and each has one job. Controllers receive HTTP requests and return responses, and they should do nothing else. Services hold the business logic, such as talking to a database or applying a rule. Modules group controllers and services that belong together, so a feature can be understood and tested as one unit.…