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Exception Filter Example - Nestjs Typing CST Test
Exception Filter Example — Nestjs Code
A custom exception filter catching HTTP errors.
import { ExceptionFilter, Catch, ArgumentsHost, HttpException, Module } from '@nestjs/common';
import { NestFactory } from '@nestjs/core';
import { Controller, Get } from '@nestjs/common';
@Catch(HttpException)
class HttpErrorFilter implements ExceptionFilter {
catch(exception: HttpException, host: ArgumentsHost) {
const ctx = host.switchToHttp();
const response = ctx.getResponse();
response.status(exception.getStatus()).json({ message: exception.message });
}
}
@Controller()
class AppController {
@Get('error') throwError() { throw new HttpException('Custom error', 400); }
}
@Module({ controllers: [AppController] })
class AppModule {}
async function bootstrap() {
const app = await NestFactory.create(AppModule);
app.useGlobalFilters(new HttpErrorFilter());
await app.listen(3000);
}
bootstrap();Nestjs Language Guide
NestJS is a progressive Node.js framework for building efficient, scalable, and maintainable server-side applications using TypeScript and modern JavaScript.
Primary Use Cases
- ▸Building RESTful APIs and GraphQL services
- ▸Creating microservices with built-in support
- ▸Developing server-side applications with TypeScript
- ▸Implementing real-time WebSocket applications
- ▸Building enterprise-grade backend systems
Notable Features
- ▸TypeScript-first design
- ▸Modular architecture
- ▸Dependency Injection container
- ▸Support for REST, GraphQL, WebSockets, and microservices
- ▸Built-in testing and CLI tools
Origin & Creator
NestJS was created by Kamil Myśliwiec in 2017 to provide a structured framework for building maintainable Node.js server-side applications with TypeScript.
Industrial Note
NestJS is popular in enterprise backend ecosystems and microservice architectures, providing scalable, modular, and maintainable server-side solutions.
Quick Explain
- ▸NestJS leverages TypeScript to provide strong typing and modern OOP/FP paradigms for Node.js backend development.
- ▸It uses the modular architecture inspired by Angular, with controllers, providers, and modules.
- ▸Supports REST APIs, GraphQL, WebSockets, microservices, and more.
- ▸Encourages best practices like dependency injection, middleware, and exception handling.
- ▸Widely used for enterprise-grade Node.js applications and complex backend systems.
Core Features
- ▸Modules, controllers, and providers for structured development
- ▸Decorators for routing, DI, and metadata
- ▸Exception filters and pipes for validation and error handling
- ▸Middleware, guards, and interceptors for request/response management
- ▸Integration with databases via TypeORM, Prisma, and Mongoose
Learning Path
- ▸Learn Node.js and TypeScript basics
- ▸Understand NestJS modules, controllers, and providers
- ▸Practice building REST APIs
- ▸Learn authentication, GraphQL, and WebSockets
- ▸Build a full-featured scalable backend
Practical Examples
- ▸Build a CRUD REST API
- ▸Implement JWT authentication
- ▸Create GraphQL resolver
- ▸Set up WebSocket chat server
- ▸Integrate a microservice with RabbitMQ
Comparisons
- ▸NestJS vs Express: structured + TypeScript vs minimalistic JS
- ▸NestJS vs Fastify: scalable + modular vs lightweight performance
- ▸NestJS vs Blazor: backend API vs full-stack C# SPA
- ▸NestJS vs Spring Boot: Node.js + TypeScript vs Java backend
- ▸NestJS vs Koa: DI and modules vs minimalistic middleware
Strengths
- ▸Strong typing with TypeScript ensures code reliability
- ▸Highly modular and scalable architecture
- ▸Integration with modern backend tools and frameworks
- ▸Supports enterprise-level patterns and practices
- ▸Comprehensive documentation and strong community support
Limitations
- ▸Steeper learning curve for developers unfamiliar with TypeScript or Angular-style patterns
- ▸Adds abstraction over raw Node.js/Express APIs
- ▸Some advanced features require understanding of decorators and DI
- ▸Initial setup may feel heavy for small projects
- ▸Less flexible than lightweight frameworks like Fastify/Express for simple apps
When NOT to Use
- ▸Small scripts or lightweight APIs
- ▸Projects that don’t use TypeScript
- ▸Apps where raw Express/Fastify is sufficient
- ▸Highly experimental projects needing minimal abstraction
- ▸Frontend-only projects
Cheat Sheet
- ▸@Controller - define routes
- ▸@Get/@Post - define HTTP method handlers
- ▸@Injectable - mark services for DI
- ▸Modules - organize features
- ▸Providers - implement business logic
FAQ
- ▸Is NestJS free?
- ▸Yes - open-source under MIT license.
- ▸Does it replace Express?
- ▸NestJS uses Express/Fastify under the hood with abstraction.
- ▸Which languages are used?
- ▸TypeScript and modern JavaScript.
- ▸Is it suitable for enterprise apps?
- ▸Yes, designed for scalable and maintainable systems.
- ▸Can it handle microservices?
- ▸Yes, built-in support for microservice architecture and messaging.
30-Day Skill Plan
- ▸Week 1: NestJS basics, simple REST API
- ▸Week 2: Services and database integration
- ▸Week 3: Authentication and authorization
- ▸Week 4: GraphQL and WebSockets
- ▸Week 5: Microservices and deployment
Final Summary
- ▸NestJS is a TypeScript-first Node.js framework for backend development.
- ▸Uses modular architecture, DI, and decorators for scalable apps.
- ▸Supports REST, GraphQL, WebSockets, and microservices.
- ▸Strong TypeScript integration ensures maintainability.
- ▸Ideal for enterprise-grade, scalable server-side applications.
Project Structure
- ▸src/ - source code
- ▸src/app.module.ts - root module
- ▸src/app.controller.ts - root controller
- ▸src/app.service.ts - root service
- ▸main.ts - bootstrap file
Monetization
- ▸Enterprise backend solutions
- ▸API-based SaaS platforms
- ▸Real-time applications (chat, trading, dashboards)
- ▸Subscription services using NestJS backend
- ▸Backend for mobile and web apps
Productivity Tips
- ▸Use Nest CLI for scaffolding
- ▸Reuse modules and providers
- ▸Leverage decorators for clean code
- ▸Write tests alongside features
- ▸Use TypeScript type-checking to prevent runtime errors
Basic Concepts
- ▸Modules encapsulate features
- ▸Controllers handle routes
- ▸Providers implement business logic
- ▸Decorators annotate classes/methods with metadata
- ▸Dependency Injection manages service instantiation