class-validator decorators in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to validate that the 'email' property is a valid email address.

NestJS

import { [1] } from 'class-validator';

class UserDto {
  @[1]()
  email: string;
}

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

AIsEmail

BIsString

CIsNotEmpty

DIsNumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using @IsString instead of @IsEmail

Forgetting to import the decorator

Using @IsNotEmpty which only checks presence, not format

The @IsEmail() decorator checks if the property is a valid email address.

2fill in blank

medium

Complete the code to ensure the 'age' property is a number and at least 18.

NestJS

import { IsNumber, [1] } from 'class-validator';

class UserDto {
  @IsNumber()
  @[1](18)
  age: number;
}

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

AMax

BIsPositive

CMin

DIsInt

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Max instead of @Min

Using @IsInt which only checks integer, not minimum value

Not combining with @IsNumber

The @Min(18) decorator ensures the number is at least 18.

3fill in blank

hard

Fix the error in the code to validate that 'username' is a non-empty string.

NestJS

import { IsString, [1] } from 'class-validator';

class UserDto {
  @IsString()
  @[1]()
  username: string;
}

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

AIsNotEmpty

BIsEmail

CIsNumber

DMinLength

Attempts:

3 left

💡 Hint

Common Mistakes

Using @MinLength without specifying length

Using @IsEmail which is for emails

Using @IsNumber on a string

The @IsNotEmpty() decorator ensures the string is not empty.

4fill in blank

hard

Fill both blanks to validate that 'password' is a string with minimum length 8.

NestJS

import { [1], [2] } from 'class-validator';

class UserDto {
  @[1]()
  @[2](8)
  password: string;
}

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

AIsString

BMinLength

CIsNotEmpty

DMaxLength

Attempts:

3 left

💡 Hint

Common Mistakes

Using @MaxLength instead of @MinLength

Forgetting to check type with @IsString

Using @IsNotEmpty which does not check length

@IsString() ensures the value is a string, and @MinLength(8) ensures it has at least 8 characters.

5fill in blank

hard

Fill all three blanks to create a validation that 'tags' is an optional array of strings with each string not empty.

NestJS

import { [1], [2], [3] } from 'class-validator';

class UserDto {
  @[1]()
  @[2]({ each: true })
  @[3]({ each: true })
  tags?: string[];
}

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

AIsOptional

BIsString

CIsNotEmpty

DIsArray

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting @IsOptional and causing validation errors when property is missing

Not using { each: true } and validating the whole array instead of items

Using @IsArray but missing item validations

@IsOptional() allows the property to be missing, @IsString({ each: true }) checks each item is a string, and @IsNotEmpty({ each: true }) ensures no empty strings in the array.