Middleware vs decorator pattern in Node.js - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

Node.js

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

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

Apath

Burl

Cbody

Dmethod

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.url instead of req.method for the HTTP method

Trying to access req.path which is not the method

Logging req.body which is the request data, not the method

The req.method property contains the HTTP method of the request, such as GET or POST. This is what we want to log along with the URL.

2fill in blank

medium

Complete the code to apply a decorator function that adds a greeting to the original function's output.

Node.js

function greet() {
  return 'World';
}

function decorator(fn) {
  return function() {
    return 'Hello ' + fn[1]();
  };
}

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

Acall

Bapply

C()

D.call

Attempts:

3 left

💡 Hint

Common Mistakes

Using fn.call without parentheses, which is a function reference, not a call

Using fn.apply which requires arguments array

Using .call as a string which is invalid syntax

To call the function fn inside the decorator, we use fn(). The parentheses () invoke the function.

3fill in blank

hard

Fix the error in the middleware function to correctly handle asynchronous operations.

Node.js

async function auth(req, res, [1]) {
  const user = await getUser(req.token);
  if (!user) {
    res.status(401).send('Unauthorized');
  } else {
    next();
  }
}

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

Anext

Bcallback

Cdone

Dproceed

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different name like done or callback which Express does not recognize

Not calling next() at all causing the request to hang

In Express middleware, the third argument is always named next. It is a function to call to pass control to the next middleware.

4fill in blank

hard

Fill both blanks to create a decorator that logs before and after calling the original function.

Node.js

function logDecorator(fn) {
  return function(...args) {
    console.[1]('Before call');
    const result = fn(...args);
    console.[2]('After call');
    return result;
  };
}

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

Alog

Bwarn

Cerror

Dinfo

Attempts:

3 left

💡 Hint

Common Mistakes

Using console.warn or console.error which are for warnings or errors

Mixing different console methods in the two blanks

The console.log method is used to print normal messages to the console. We want to log both before and after the function call.

5fill in blank

hard

Fill all three blanks to create middleware that checks for a token and calls next or sends error.

Node.js

function checkToken(req, res, [1]) {
  const token = req.headers['[2]'];
  if (!token) {
    res.status([3]).send('Token missing');
  } else {
    next();
  }
}

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

Anext

Bauthorization

C401

Dtoken

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong header name like 'token' instead of 'authorization'

Using wrong status code like 403 instead of 401

Naming the third argument incorrectly

The third middleware argument is next. The token is usually in the authorization header. The status code for missing token is 401 Unauthorized.