NestJS (also called Nest) is an open-source framework for building server-side applications on Node.js, the runtime that runs JavaScript outside the browser. A framework gives a program its structure: the developer writes the parts, and the framework connects and calls them. Nest is built with TypeScript, a typed form of JavaScript, and stays compatible with plain JavaScript. Its author is Kamil Myśliwiec.
A Nest application is organized into self-contained modules. Built-in dependency injection creates the objects that a class needs and passes them in, which makes code easier to maintain and test. TypeScript decorators, labels written above a class or method, declare the role of each part. Under the hood Nest uses Express, a Node.js web server library, and it also works with Fastify. It supports microservice architectures, in which an application is split into small services that talk over a network. The code style combines object-oriented, functional and functional reactive programming.
Nest is free under the MIT license and is funded by sponsors. The team sells enterprise support, online courses and add-on tools for observability and for deployment to AWS.