Middleware testing strategies in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple Express middleware function that logs the request method.

Express

function logger(req, res, [1]) {
  console.log(req.method);
  next();
}

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

Ahandle

Bdone

Ccallback

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter names like 'done' or 'callback' instead of 'next'.

Forgetting to call the next function.

The middleware function must include next as the third parameter to pass control to the next middleware.

2fill in blank

medium

Complete the code to test an Express middleware that adds a property to the request object.

Express

const req = {};
const res = {};
const next = () => {};
middleware(req, res, [1]);
console.log(req.customProperty);

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

Adone

Bnext

Ccallback

Dhandle

Attempts:

3 left

💡 Hint

Common Mistakes

Passing incorrect function names instead of 'next'.

Not passing a function as the third argument.

When testing middleware, you call it with req, res, and a next function to simulate Express behavior.

3fill in blank

hard

Fix the error in the test code that checks if middleware calls next with an error.

Express

middleware(req, res, (err) => {
  if (err) {
    console.log('Error handled');
  }
  [1];
});

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

Areturn

Bthrow err

Cnext()

Dconsole.error(err)

Attempts:

3 left

💡 Hint

Common Mistakes

Calling next() inside the error handler callback.

Throwing the error instead of handling it.

Using return here stops further execution after handling the error, which is correct in this test callback.

4fill in blank

hard

Fill both blanks to create a test that verifies middleware modifies the response and calls next.

Express

const res = {
  statusCode: 200,
  [1]: function(code) {
    this.statusCode = code;
    return this;
  }
};

middleware(req, res, [2]);

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

Astatus

Bnext

Csend

Ddone

Attempts:

3 left

💡 Hint

Common Mistakes

Using send instead of status for setting status code.

Passing incorrect function names instead of next.

The res.status method sets the status code and returns res for chaining. The next function is passed to middleware to continue processing.

5fill in blank

hard

Fill all three blanks to test middleware that conditionally skips to next middleware.

Express

function testMiddleware(req, res, [1]) {
  if (!req.user) {
    [2]();
    return;
  }
  res.message = 'User found';
  [3]();
}

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

Anext

Bdone

Dcallback

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the next function parameter and calls.

Not calling next() to continue middleware chain.

The middleware uses next to skip or continue. The first and second blanks are the next function parameter and call. The third blank is also a call to next to continue processing.