Custom pipes in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a custom pipe class in NestJS.

NestJS

import { PipeTransform, Injectable } from '@nestjs/common';

@Injectable()
export class ParseIntPipe implements [1] {
  transform(value: any) {
    return parseInt(value, 10);
  }
}

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AController

BPipeTransform

CModule

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Controller or @Module decorators instead of @Injectable.

Not implementing PipeTransform interface.

The custom pipe class must implement the PipeTransform interface to define the transform method.

2fill in blank

medium

Complete the code to throw an exception if the value is not a number in the custom pipe.

NestJS

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

@Injectable()
export class ParseIntPipe implements PipeTransform {
  transform(value: any) {
    const val = parseInt(value, 10);
    if (isNaN(val)) {
      throw new [1]('Validation failed');
    }
    return val;
  }
}

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ANotFoundException

BHttpException

CUnauthorizedException

DBadRequestException

Attempts:

3 left

💡 Hint

Common Mistakes

Throwing exceptions unrelated to validation like NotFoundException.

Not throwing any exception on invalid input.

BadRequestException is used to indicate that the client sent invalid data.

3fill in blank

hard

Fix the error in the custom pipe to correctly implement the transform method signature.

NestJS

import { PipeTransform, Injectable, ArgumentMetadata } from '@nestjs/common';

@Injectable()
export class ParseIntPipe implements PipeTransform {
  transform(value: any, [1]) {
    const val = parseInt(value, 10);
    if (isNaN(val)) {
      throw new Error('Validation failed');
    }
    return val;
  }
}

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Acontext: ExecutionContext

Bargs: any[]

Cmetadata: ArgumentMetadata

Drequest: Request

Attempts:

3 left

💡 Hint

Common Mistakes

Using ExecutionContext which is for guards and interceptors.

Omitting the second parameter or using wrong types.

The transform method receives the value and an ArgumentMetadata object describing the parameter.

4fill in blank

hard

Fill both blanks to apply the custom pipe to a controller route parameter.

NestJS

import { Controller, Get, Param } from '@nestjs/common';
import { ParseIntPipe } from './parse-int.pipe';

@Controller('items')
export class ItemsController {
  @Get(':id')
  findOne(@Param('[1]', [2]) id: number) {
    return `Item #${id}`;
  }
}

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Aid

BParseIntPipe

Cbody

DValidationPipe

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter name like 'body'.

Applying a different pipe than the custom one.

The route parameter name is 'id' and the custom pipe ParseIntPipe is applied to transform it.

5fill in blank

hard

Fill all three blanks to create a reusable custom pipe that validates a positive integer.

NestJS

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

@Injectable()
export class PositiveIntPipe implements PipeTransform {
  transform(value: any) {
    const val = parseInt([1], 10);
    if (isNaN(val) || val [2] 0) {
      throw new [3]('Value must be a positive integer');
    }
    return val;
  }
}

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Avalue

B<=

CBadRequestException

Dvalue.toString()

Attempts:

3 left

💡 Hint

Common Mistakes

Parsing the raw value without converting to string.

Using wrong comparison operator.

Throwing generic Error instead of BadRequestException.

Convert value to string before parsing, check if val is less or equal to zero, and throw BadRequestException on failure.