Exception Handling

Built-in exceptions

NestJS provides BadRequestException, NotFoundException, UnauthorizedException, etc. that automatically set the right HTTP status.

import { NotFoundException, BadRequestException } from '@nestjs/common';

@Get(':id')
findOne(@Param('id') id: string) {
  const user = this.usersService.findOne(id);
  if (!user) {
    throw new NotFoundException(`User ${id} not found`);
  }
  return user;
}

Global exception filter

Implement ExceptionFilter to catch and format errors globally across your app.

@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    const status = exception instanceof HttpException ? exception.getStatus() : 500;

    response.status(status).json({
      statusCode: status,
      message: exception instanceof Error ? exception.message : 'Internal error'
    });
  }
}

// app.useGlobalFilters(new AllExceptionsFilter());

Throwing HTTP exceptions

Throw a built-in exception and Nest builds the response.

• NotFoundException maps to status 404.
• The message you pass becomes the message field.

import { Controller, Get, NotFoundException, Param } from '@nestjs/common';

@Controller('books')
export class BooksController {
  @Get(':id')
  find(@Param('id') id: string) {
    throw new NotFoundException(`Book ${id} not found`);
  }
}

Output:

{"message":"Book 5 not found","error":"Not Found","statusCode":404}

Quick check

Quick check: What does `@Catch()` with no arguments on an exception filter catch?

• Only HttpException
• Every thrown exception
• Only validation errors