Error response formatting in Node.js - Mini Project: Build & Apply

Error Response Formatting in Node.js

📖 Scenario: You are building a simple Node.js server that sends error responses in a consistent JSON format. This helps clients understand what went wrong.

🎯 Goal: Create a Node.js server that returns error responses with a JSON object containing status, message, and errorCode fields.

📋 What You'll Learn

Create an error object with specific properties

Add a configuration variable for default error code

Write a function to format the error response JSON

Send the formatted error response in the server

💡 Why This Matters

🌍 Real World

APIs and web servers need to send clear, consistent error messages so clients can handle problems properly.

💼 Career

Understanding error response formatting is essential for backend developers working with Node.js and building reliable web services.

1

Create the error object

Create a constant called error with these exact properties: status set to 400, message set to "Invalid input", and errorCode set to "INVALID_INPUT".

Node.js

// Your code here

Need a hint?

Use const error = { status: 400, message: "Invalid input", errorCode: "INVALID_INPUT" }.

2

Add default error code configuration

Create a constant called DEFAULT_ERROR_CODE and set it to the string "UNKNOWN_ERROR".

Node.js

const error = {
  status: 400,
  message: "Invalid input",
  errorCode: "INVALID_INPUT"
};

// Your code here

Need a hint?

Use const DEFAULT_ERROR_CODE = "UNKNOWN_ERROR"; to set the default error code.

3

Write the error formatting function

Write a function called formatErrorResponse that takes an error object as input and returns a new object with status, message, and errorCode. Use the errorCode from the input error if it exists; otherwise, use DEFAULT_ERROR_CODE.

Node.js

const error = {
  status: 400,
  message: "Invalid input",
  errorCode: "INVALID_INPUT"
};

const DEFAULT_ERROR_CODE = "UNKNOWN_ERROR";

// Your code here

Need a hint?

Use error.errorCode || DEFAULT_ERROR_CODE to provide a fallback error code.

4

Send the formatted error response in a Node.js server

Create a simple Node.js HTTP server using http.createServer. In the request handler, use formatErrorResponse(error) to get the error JSON, set the response header Content-Type to application/json, and send the JSON stringified error response with the status code from error.status.

Node.js

const error = {
  status: 400,
  message: "Invalid input",
  errorCode: "INVALID_INPUT"
};

const DEFAULT_ERROR_CODE = "UNKNOWN_ERROR";

function formatErrorResponse(error) {
  return {
    status: error.status,
    message: error.message,
    errorCode: error.errorCode || DEFAULT_ERROR_CODE
  };
}

// Your code here

Need a hint?

Use http.createServer and res.writeHead with Content-Type set to application/json.