Pipe binding (parameter, method, controller, global) in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to bind a pipe to a single parameter in a NestJS controller method.

NestJS

async getUser(@Param('id', [1]) id: number) { return this.userService.findById(id); }

Drag options to blanks, or click blank then click option'

Aid

BParseIntPipe

CBody

DQuery

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting 'id' (the parameter name) instead of a pipe like ParseIntPipe

Confusing pipes with other decorators like @Body or @Query

To bind a pipe to a single parameter, provide the pipe class as the second argument to the @Param decorator, such as ParseIntPipe to convert the string ID to a number.

2fill in blank

medium

Complete the code to apply a pipe to an entire controller method.

NestJS

@UsePipes([1])
async create(@Body() data: CreateDto) { return this.service.create(data); }

Drag options to blanks, or click blank then click option'

AController

BParseIntPipe

CHttpException

DValidationPipe

Attempts:

3 left

💡 Hint

Common Mistakes

Using a class that is not a pipe inside @UsePipes

Confusing @UsePipes with @UseGuards or other decorators

UsePipes decorator applies the specified pipe(s) to the whole method; ValidationPipe is commonly used for DTO validation.

3fill in blank

hard

Fix the error in binding a pipe globally in the main.ts file.

NestJS

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.useGlobalPipes(new [1]());
  await app.listen(3000);
}

Drag options to blanks, or click blank then click option'

AValidationPipe

BParseIntPipe

CHttpException

DController

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-pipe classes like Controller or HttpException

Forgetting to instantiate the pipe with 'new'

ValidationPipe is the correct pipe to use globally for validating all incoming requests.

4fill in blank

hard

Fill both blanks to bind a pipe to a controller and a method.

NestJS

@UsePipes([1])
@Controller('items')
export class ItemsController {
  @UsePipes([2])
  async update(@Param('id', ParseIntPipe) id: number) {
    return this.itemsService.update(id);
  }
}

Drag options to blanks, or click blank then click option'

AValidationPipe

BParseIntPipe

CHttpException

DController

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-pipe classes in @UsePipes

Mixing up controller and method pipe usage

ValidationPipe is applied at the controller level for general validation; ParseIntPipe is applied at the method level to parse the 'id' parameter.

5fill in blank

hard

Fill all three blanks to create a custom pipe and bind it globally.

NestJS

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

@Injectable()
export class [1] implements PipeTransform {
  transform(value: any, metadata: ArgumentMetadata) {
    if (!value) {
      throw new [2]('Value is required');
    }
    return value.trim();
  }
}

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.useGlobalPipes(new [3]());
  await app.listen(3000);
}

Drag options to blanks, or click blank then click option'

ATrimPipe

BBadRequestException

DValidationPipe

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong exception class

Not instantiating the pipe with 'new' when binding globally

Mismatching class names

TrimPipe is the custom pipe class name; BadRequestException is thrown on invalid input; the global pipe instance is created with new TrimPipe().

Practice

1. What is the main purpose of binding a pipe to a parameter in NestJS?

easy

A. To define routing paths for the controller methods

B. To apply middleware logic before the controller handles the request

C. To globally change all incoming requests in the application

D. To transform or validate the specific parameter before the method uses it

Solution

1. Step 1: Understand parameter-level pipe binding

   Binding a pipe to a parameter means the pipe runs only on that parameter to transform or validate it before the method uses it.

2. Step 2: Differentiate from other bindings

   Middleware and global pipes affect broader scopes, not just a single parameter. Routing is unrelated to pipes.

3. Final Answer:

   To transform or validate the specific parameter before the method uses it -> Option D

4. Quick Check:

   Parameter pipe = transform/validate parameter [OK]

Hint: Parameter pipes affect only one input value [OK]

Common Mistakes:

• Confusing parameter pipes with global pipes
• Thinking pipes define routes
• Mixing middleware with pipes

2. Which of the following is the correct syntax to bind a pipe globally in a NestJS application?

easy

A. @UsePipes(new ValidationPipe()) on a controller class

B. app.useGlobalPipes(new ValidationPipe());

C. @UsePipes(new ValidationPipe()) on a method

D. Bind pipe inside a method parameter decorator

Solution

1. Step 1: Identify global pipe binding syntax

   Global pipes are bound using the app instance with app.useGlobalPipes(pipeInstance).

2. Step 2: Differentiate from controller and method bindings

   @UsePipes decorator applies pipes at controller or method level, not globally.

3. Final Answer:

   app.useGlobalPipes(new ValidationPipe()); -> Option B

4. Quick Check:

   Global pipe = app.useGlobalPipes() [OK]

Hint: Global pipes use app.useGlobalPipes() method [OK]

Common Mistakes:

• Using @UsePipes for global binding
• Binding pipes inside method parameters for global effect
• Confusing middleware with pipes

3. Given the following code, what will be the output if the incoming request has a query parameter age='25' (string)?

import { Controller, Get, Query, ParseIntPipe } from '@nestjs/common';

@Controller('users')
export class UserController {
  @Get()
  getUser(@Query('age', ParseIntPipe) age: number) {
    return { age, type: typeof age };
  }
}

medium

A. Runtime error due to type mismatch

B. {"age": "25", "type": "string"}

C. {"age": 25, "type": "number"}

D. {"age": null, "type": "object"}

Solution

1. Step 1: Understand ParseIntPipe effect on query parameter

   ParseIntPipe converts the string '25' to the number 25 before passing it to the method.

2. Step 2: Check returned object values

   The method returns an object with age as number 25 and type as 'number'.

3. Final Answer:

   {"age": 25, "type": "number"} -> Option C

4. Quick Check:

   ParseIntPipe converts string to number [OK]

Hint: ParseIntPipe converts string query to number [OK]

Common Mistakes:

• Assuming age remains string
• Expecting runtime error on conversion
• Confusing type of returned value

4. Identify the error in this NestJS controller code snippet where a pipe is bound at the method level:

import { Controller, Get, UsePipes, ValidationPipe, Query } from '@nestjs/common';

@Controller('products')
export class ProductController {
  @Get()
  @UsePipes(ValidationPipe)
  findProduct(@Query('id') id: string) {
    return id;
  }
}

medium

A. ValidationPipe should be instantiated with 'new' keyword in @UsePipes

B. @UsePipes cannot be used on methods, only on controllers

C. Query decorator is missing a pipe binding

D. Controller decorator is missing parameters

Solution

1. Step 1: Check @UsePipes decorator usage

   @UsePipes expects an instance of a pipe, so ValidationPipe must be called with 'new'.

2. Step 2: Validate other parts

   @UsePipes can be used on methods, Query decorator is valid, Controller decorator is correct.

3. Final Answer:

   ValidationPipe should be instantiated with 'new' keyword in @UsePipes -> Option A

4. Quick Check:

   @UsePipes needs pipe instances [OK]

Hint: Always instantiate pipes with 'new' in decorators [OK]

Common Mistakes:

• Passing pipe class instead of instance
• Thinking @UsePipes only works on controllers
• Missing pipe on parameter is not an error

5. You want to apply a custom pipe that trims whitespace from all string inputs in a controller and also validate numbers globally. Which binding strategy is best to achieve this cleanly?

hard

A. Bind the trim pipe at controller level and the number validation pipe globally

B. Bind both pipes globally to affect all controllers and methods

C. Bind both pipes only on method parameters where needed

D. Bind the trim pipe globally and the number validation pipe at method level

Solution

1. Step 1: Understand scope of pipes for separation of concerns

   Trimming strings is specific to this controller's inputs, so controller-level binding keeps it scoped and clean.

2. Step 2: Apply number validation globally

   Number validation is common across the app, so global binding ensures consistent validation everywhere.

3. Final Answer:

   Bind the trim pipe at controller level and the number validation pipe globally -> Option A

4. Quick Check:

   Controller pipe for specific, global pipe for common validation [OK]

Hint: Use controller pipes for specific, global pipes for common tasks [OK]

Common Mistakes:

• Binding all pipes globally causing unnecessary processing
• Binding all pipes only on parameters causing repetition
• Mixing global and method-level without clear reason