class-transformer usage in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to transform a plain object into a class instance using class-transformer.

NestJS

import { plainToInstance } from 'class-transformer';

class User {
  name: string;
  age: number;
}

const plainUser = { name: 'Alice', age: 25 };
const user = plainToInstance(User, [1]);
console.log(user instanceof User);

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

AplainUser

Bnew User()

C{ name: 'Bob', age: 30 }

DUser

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the class name instead of the object.

Passing a new instance instead of the plain object.

The plainToInstance function converts a plain object into an instance of the given class. Here, we pass the plainUser object to transform it into a User instance.

2fill in blank

medium

Complete the code to exclude the password field when transforming a User object to plain using class-transformer.

NestJS

import { Exclude, plainToInstance, instanceToPlain } from 'class-transformer';

class User {
  name: string;
  @Exclude()
  [1]: string;
}

const user = plainToInstance(User, { name: 'Bob', password: 'secret' });
const plainUser = instanceToPlain(user);
console.log(plainUser);

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

Asecret

Bname

Cage

Dpassword

Attempts:

3 left

💡 Hint

Common Mistakes

Excluding the wrong property like name or age.

Trying to exclude a value instead of a property name.

The @Exclude() decorator hides the password property when converting the class instance back to a plain object.

3fill in blank

hard

Fix the error in the code to properly transform nested objects using class-transformer.

NestJS

import { Type, plainToInstance } from 'class-transformer';

class Photo {
  url: string;
}

class User {
  name: string;
  @Type(() => [1])
  photos: Photo[];
}

const plainUser = {
  name: 'Alice',
  photos: [{ url: 'photo1.jpg' }, { url: 'photo2.jpg' }]
};

const user = plainToInstance(User, plainUser);
console.log(user.photos[0] instanceof Photo);

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

AString

BPhoto

CUser

DObject

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong class in @Type decorator.

Omitting the @Type decorator for nested objects.

The @Type decorator tells class-transformer which class to use for nested objects. Here, it should be Photo for the photos array.

4fill in blank

hard

Fill both blanks to create a class-transformer transformer that converts a string to a number during transformation.

NestJS

import { Transform, plainToInstance } from 'class-transformer';

class Product {
  @Transform(({ value }) => [1])
  price: number;
}

const plainProduct = { price: '100' };
const product = plainToInstance(Product, plainProduct);
console.log(typeof product.price === [2]);

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ANumber(value)

B'number'

C'string'

DparseInt(value)

Attempts:

3 left

💡 Hint

Common Mistakes

Using parseInt without returning the value.

Checking typeof against 'string' instead of 'number'.

The Transform decorator converts the string value to a number using Number(value). The typeof operator returns 'number' for numeric types.

5fill in blank

hard

Fill all three blanks to create a class-transformer setup that excludes a field, transforms a nested object, and converts a string to a boolean.

NestJS

import { Exclude, Type, Transform, plainToInstance } from 'class-transformer';

class Settings {
  @Transform(({ value }) => [1])
  darkMode: boolean;
}

class User {
  name: string;
  @Exclude()
  [2]: string;
  @Type(() => [3])
  settings: Settings;
}

const plainUser = {
  name: 'Eve',
  password: '1234',
  settings: { darkMode: 'true' }
};

const user = plainToInstance(User, plainUser);
console.log(user.password === undefined);
console.log(typeof user.settings.darkMode === 'boolean');

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

Avalue === 'true'

Bpassword

CSettings

DdarkMode

Attempts:

3 left

💡 Hint

Common Mistakes

Not excluding the password field properly.

Not converting the darkMode string to boolean.

Not using the correct class in @Type decorator.

The Transform converts the string 'true' to boolean true. The password field is excluded with @Exclude. The settings field is transformed to a Settings instance using @Type.