Custom pipes in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom pipe in NestJS?

A custom pipe in NestJS is a class that implements the PipeTransform interface to transform or validate data before it reaches the route handler.

beginner

Which method must be implemented in a custom pipe class?

The method transform(value: any, metadata: ArgumentMetadata) must be implemented to define how the input data is processed.

beginner

How do you apply a custom pipe to a route handler parameter?

You apply a custom pipe by adding it as an argument decorator, for example: @Param('id', new MyCustomPipe()) id: string.

intermediate

What happens if a custom pipe throws an exception during transformation?

If a custom pipe throws an exception, NestJS stops the request processing and sends an error response to the client.

intermediate

Why use custom pipes instead of handling validation inside controllers?

Custom pipes keep controllers clean by separating validation and transformation logic, making code easier to maintain and reuse.

What interface must a custom pipe implement in NestJS?

A PipeTransform

B PipeInterface

C Transformable

D Validator

Custom pipes must implement the PipeTransform interface to define the transform method.

Where is the transform method called in a custom pipe?

A During module initialization

B After the response is sent

C Before the route handler executes

D Inside the controller constructor

The transform method runs before the route handler to process incoming data.

How do you apply a custom pipe globally in NestJS?

A Import it in the module providers

B Add it to the controller constructor

C Use @GlobalPipe decorator

D Use app.useGlobalPipes(new MyPipe())

Global pipes are applied with app.useGlobalPipes() in the main bootstrap file.

What should a custom pipe return if the input is valid?

A Throw an exception

B The transformed or original value

C Null

D Undefined

If valid, the pipe returns the transformed or original value to continue processing.

Which decorator is commonly used to apply a pipe to a route parameter?

A All of the above

B @Body

C @Query

D @Param

Pipes can be applied to @Param, @Body, and @Query decorators to validate or transform data.

Explain how to create and use a custom pipe in NestJS.

Think about how data flows before reaching the controller.

Describe the benefits of using custom pipes for validation and transformation.

Consider how code organization improves with pipes.