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Introduction to NestJS

NestJS is a progressive Node.js framework designed for building efficient, reliable, and scalable server-side (backend) applications. It is natively built with TypeScript and combines elements of Object-Oriented Programming (OOP), Functional Programming (FP), and Functional Reactive Programming (FRP).

1. Conceptual Foundations and Architecture​

NestJS provides an out-of-the-box application architecture that allows developers and teams to create highly testable, scalable, loosely coupled, and easily maintainable applications. It draws heavy inspiration from proven design patterns in enterprise development, such as Dependency Injection (DI) and controller-service architecture (similar to Angular or Spring Boot).

A. Request Lifecycle​

In NestJS, incoming HTTP requests pass through a series of sequentially organized layers before a response is sent back to the client. Each layer serves a specific purpose within the application architecture:

Technical Explanation of Lifecycle Layers:​

  • Middlewares: Functions executed before the route handler. They have access to the request (req) and response (res) objects. Commonly used for tasks like logging, body parsing, or header validation.
  • Guards: Determine whether a given request will be handled by the controller based on specific conditions (such as user authentication or role-based permissions).
  • Interceptors: Allow binding extra logic before or after target method execution, transforming function results, or extending basic behavior.
  • Pipes: Used for two main use cases: transformation (converting input data to desired formats, like string to number) and validation (evaluating if input data is valid according to DTO rules).
  • Controllers: Responsible for receiving incoming requests, processing HTTP routes (GET, POST, PUT, DELETE), and returning appropriate responses to the client.
  • Services (Providers): Contain pure application business logic. Injected into controllers using Dependency Injection.
  • Exception Filters: Capture all unhandled errors thrown across the application to process and return a clean, standardized HTTP error response to the client.

2. Visual Resources and Cheatsheet​

Below you can check the interactive presentation for this module and the official cheatsheet with key NestJS commands and instructions.


3. Self-Assessment Quiz​

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