Request context middleware in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a middleware function that adds a context object to the request.

Express

function contextMiddleware(req, res, next) {
  req.[1] = {};
  next();
}

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

Acontext

Bdata

Cinfo

Dstate

Attempts:

3 left

💡 Hint

Common Mistakes

Using a property name that conflicts with existing Express properties.

Forgetting to call next() to continue the middleware chain.

The middleware adds a context object to the req so other handlers can store data there.

2fill in blank

medium

Complete the code to attach a user ID to the request context inside the middleware.

Express

function contextMiddleware(req, res, next) {
  req.context = {};
  req.context.[1] = req.headers['x-user-id'];
  next();
}

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

Auid

Buser

Cid

DuserId

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic name like id which may be ambiguous.

Not reading the user ID from the correct header.

We store the user ID under userId in the context for clarity.

3fill in blank

hard

Fix the error in the middleware to ensure the context is initialized only once per request.

Express

function contextMiddleware(req, res, next) {
  if (!req.[1]) {
    req.context = {};
  }
  next();
}

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

Acontext

Bctx

Cstate

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Checking a different property name than the one used to store context.

Not guarding initialization causing data loss.

We check if req.context exists before initializing to avoid overwriting.

4fill in blank

hard

Fill both blanks to create a middleware that adds a timestamp and a request ID to the context.

Express

function contextMiddleware(req, res, next) {
  req.context = {
    [1]: Date.now(),
    [2]: req.headers['x-request-id']
  };
  next();
}

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

Atimestamp

BrequestId

CreqId

Dtime

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent or unclear property names.

Not reading the request ID from the correct header.

We use timestamp for the current time and requestId for the unique request identifier.

5fill in blank

hard

Fill all three blanks to create a middleware that initializes context, sets a user role, and logs the context.

Express

function contextMiddleware(req, res, next) {
  req.[1] = {};
  req.context.[2] = req.headers['x-user-role'] || 'guest';
  console.log('Context:', req.[3]);
  next();
}

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

Acontext

Brole

Dstate

Attempts:

3 left

💡 Hint

Common Mistakes

Using different property names for context initialization and logging.

Forgetting to provide a default user role.

The context is initialized on req.context. The user role is stored as role. The console logs the context property.