nestjs-exception-handler

NestJS Exception Handler

A production-grade global exception handling system for NestJS applications that provides consistent global error response format for all types of errors.

Why This Package Exists

When building NestJS applications, error handling can become inconsistent across different scenarios:

• ValidationPipe errors from class-validator
• HttpException thrown manually
• Prisma database errors
• Unexpected internal server errors

This package ensures every error response follows the same standardized format, making your API consistent and easier to consume by clients.

Features

• Standardized Error Responses: Consistent error format across your entire application
• ValidationPipe Support: Automatic extraction and normalization of class-validator errors
• Prisma Integration: Built-in support for Prisma error codes (P2002, P2003, P2005, P2006, P2025)
• HttpException Handling: Handles all NestJS HTTP exceptions with proper formatting
• 404 Route Handling: Converts unmatched routes to standardized format
• Unknown Error Handling: Safe fallback for unexpected errors without leaking stack traces
• Extensible: Plugin system for custom formatters
• Type Safe: Full TypeScript support with zero any types
• Production Ready: Configurable logging and stack trace control
• NestJS v9 & v10 Compatible: Works with both major versions

Installation

npm install nestjs-exception-handler

Or with yarn:

yarn add nestjs-exception-handler

Quick Setup

1. Apply the Global Filter

The simplest way to use the package is to apply the global exception filter:

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { GlobalExceptionFilter } from 'nestjs-exception-handler';
import { ValidationPipe } from '@nestjs/common';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);

  app.useGlobalPipes(
    new ValidationPipe({
      whitelist: true,
      transform: true,
    }),
  );

  app.useGlobalFilters(new GlobalExceptionFilter());

  await app.listen(3000);
}
bootstrap();

2. Using with Module Registration (Optional)

For more control, you can use the module registration:

import { Module } from '@nestjs/common';
import { ExceptionHandlerModule } from 'nestjs-exception-handler';

@Module({
  imports: [
    ExceptionHandlerModule.forRoot({
      enableLogging: true,
      hideStackTrace: true,
    }),
  ],
})
export class AppModule {}

Error Response Format

Every error response follows this exact structure:

interface ErrorResponse {
  success: false;
  message: string;
  errorMessages: {
    path: string;
    message: string[];
  }[];
}

Example Response

{
  "success": false,
  "message": "Bad Request Exception",
  "errorMessages": [
    {
      "path": "http_error",
      "message": ["email must be an email", "password must be longer than 8 characters"]
    }
  ]
}

Validation Example

When using ValidationPipe with class-validator, errors are automatically normalized:

// DTO
import { IsEmail, IsString, MinLength } from 'class-validator';

export class CreateUserDto {
  @IsEmail()
  email: string;

  @IsString()
  @MinLength(8)
  password: string;
}

Response:

{
  "success": false,
  "message": "Bad Request Exception",
  "errorMessages": [
    {
      "path": "http_error",
      "message": ["email must be an email", "password must be longer than or equal to 8 characters"]
    }
  ]
}

HttpException Example

Throwing HTTP exceptions manually:

throw new BadRequestException('User already exists');

Response:

{
  "success": false,
  "message": "Bad Request Exception",
  "errorMessages": [
    {
      "path": "http_error",
      "message": ["User already exists"]
    }
  ]
}

Other supported HTTP exceptions:

• NotFoundException - Returns "Not Found Exception"
• UnauthorizedException - Returns "Unauthorized Exception"
• ForbiddenException - Returns "Forbidden Exception"
• ConflictException - Returns "Conflict Exception"
• And all other NestJS HTTP exceptions

Prisma Error Example

The package automatically handles common Prisma errors:

P2002 - Unique Constraint Violation

// When trying to create a user with duplicate email

Response:

{
  "success": false,
  "message": "Database error",
  "errorMessages": [
    {
      "path": "email",
      "message": ["A record with this email already exists."]
    }
  ]
}

P2003 - Foreign Key Constraint

Response:

{
  "success": false,
  "message": "Database error",
  "errorMessages": [
    {
      "path": "userId",
      "message": ["The referenced userId does not exist."]
    }
  ]
}

P2025 - Record Not Found

Response:

{
  "success": false,
  "message": "Database error",
  "errorMessages": [
    {
      "path": "record",
      "message": ["The requested record does not exist."]
    }
  ]
}

Unknown Error Example

For unexpected errors:

{
  "success": false,
  "message": "Internal Server Error",
  "errorMessages": [
    {
      "path": "server",
      "message": ["Something went wrong"]
    }
  ]
}

Stack traces are never leaked in production (configurable).

404 Route Not Found Example

When a client requests a route that doesn't exist, the package automatically converts it to the standardized format:

{
  "success": false,
  "message": "Route Not Found",
  "errorMessages": [
    {
      "path": "route",
      "message": ["Cannot GET /users/test"]
    }
  ]
}

The response includes:

• The HTTP method (GET, POST, PATCH, DELETE, etc.)
• The requested URL path

Examples for Different Methods

POST to non-existent route:

{
  "success": false,
  "message": "Route Not Found",
  "errorMessages": [
    {
      "path": "route",
      "message": ["Cannot POST /api/user/test"]
    }
  ]
}

DELETE on non-existent route:

{
  "success": false,
  "message": "Route Not Found",
  "errorMessages": [
    {
      "path": "route",
      "message": ["Cannot DELETE /api/items/123"]
    }
  ]
}

Best Practices

1. Always Use Global ValidationPipe

app.useGlobalPipes(
  new ValidationPipe({
    whitelist: true,
    transform: true,
    forbidNonWhitelisted: true,
  }),
);

2. Configure Based on Environment

const config =
  process.env.NODE_ENV === 'production'
    ? { enableLogging: true, hideStackTrace: true }
    : { enableLogging: true, hideStackTrace: false };

app.useGlobalFilters(new GlobalExceptionFilter(config));

3. Create Custom Formatters

Extend the package for custom error handling:

import { ExceptionFormatter, ErrorMessage } from 'nestjs-exception-handler';

export class CustomExceptionFormatter implements ExceptionFormatter {
  supports(exception: unknown): boolean {
    return exception instanceof CustomError;
  }

  format(exception: unknown): ErrorMessage[] {
    const error = exception as CustomError;
    return [
      {
        path: error.field,
        message: [error.message],
      },
    ];
  }

  message(_exception: unknown): string {
    return 'Custom error occurred';
  }
}

API Reference

GlobalExceptionFilter

// Constructor
new GlobalExceptionFilter(service: ExceptionHandlerService, config?: ExceptionHandlerConfig)

// Config options
interface ExceptionHandlerConfig {
  enableLogging?: boolean;  // Default: true
  hideStackTrace?: boolean; // Default: false
}

ExceptionHandlerModule

// Register globally
ExceptionHandlerModule.forRoot(config?)

// Register for specific feature
ExceptionHandlerModule.forFeature(config?)

ExceptionHandlerService

// Register custom formatter
service.registerFormatter(formatter: ExceptionFormatter)

// Format exception
service.formatException(exception: unknown): { errors: ErrorMessage[]; message: string }

// Get all registered formatters
service.getAllFormatters(): ExceptionFormatter[]

Response Examples Summary

Error Type	Example
Validation	message: ["email must be an email"]
HttpException	message: ["User already exists"]
Prisma P2002	message: ["A record with this email already exists."]
404 Not Found	message: ["Cannot GET /unknown-route"]
Unknown	message: ["Something went wrong"]

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

• Fork the repository
• Create your feature branch (git checkout -b feature/amazing-feature)
• Commit your changes (git commit -m 'Add some amazing feature')
• Push to the branch (git push origin feature/amazing-feature)
• Open a Pull Request

License

MIT

Author

Nurul Islam Rimon

• GitHub: nurulislamrimon