Response transformation in NestJS - Mini Project: Build & Apply

Response Transformation in NestJS

📖 Scenario: You are building a simple NestJS API that returns user data. You want to transform the response so that only specific fields are sent back to the client, hiding sensitive information.

🎯 Goal: Create a NestJS controller that returns user data. Use response transformation to send only the id and name fields in the response, excluding password and email.

📋 What You'll Learn

Create a user data object with id, name, email, and password fields

Add a configuration variable to specify which fields to include in the response

Use a method to transform the user data to include only the specified fields

Return the transformed user data from a NestJS controller method

💡 Why This Matters

🌍 Real World

APIs often need to hide sensitive data like passwords or emails before sending responses to clients. Response transformation helps control what data is exposed.

💼 Career

Backend developers use response transformation to secure APIs and improve data privacy, which is critical in real-world applications.

1

Create the user data object

Create a constant called user with these exact fields and values: id: 1, name: 'Alice', email: '[e-mail]', password: 'secret'.

NestJS

# Create the user data object
# Your code here

Need a hint?

Use a const object with the exact keys and values.

2

Add a configuration for included fields

Create a constant called fieldsToInclude and set it to an array containing the strings 'id' and 'name'.

NestJS

const user = {
  id: 1,
  name: 'Alice',
  email: '[e-mail]',
  password: 'secret'
};

# Create the fieldsToInclude array
# Your code here

Need a hint?

Use an array with the exact strings 'id' and 'name'.

3

Create a function to transform the user data

Create a function called transformUser that takes a user object and returns a new object containing only the keys in fieldsToInclude. Use fieldsToInclude.forEach to copy fields.

NestJS

const user = {
  id: 1,
  name: 'Alice',
  email: '[e-mail]',
  password: 'secret'
};

const fieldsToInclude = ['id', 'name'];

# Create transformUser function
# Your code here

Need a hint?

Use a new object and copy only the allowed fields using forEach.

4

Return the transformed user from a NestJS controller method

Create a NestJS controller class called UserController with a method getUser that returns the result of transformUser(user). Use the @Controller('user') and @Get() decorators.

NestJS

const user = {
  id: 1,
  name: 'Alice',
  email: '[e-mail]',
  password: 'secret'
};

const fieldsToInclude = ['id', 'name'];

function transformUser(user) {
  const transformed = {};
  fieldsToInclude.forEach(field => {
    transformed[field] = user[field];
  });
  return transformed;
}

# Create UserController with getUser method
# Your code here

Need a hint?

Use NestJS decorators @Controller and @Get and return the transformed user.