req.query for query strings in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the query string parameter named 'name'.

Express

app.get('/hello', (req, res) => {
  const userName = req.[1].name;
  res.send(`Hello, ${userName}!`);
});

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

Aquery

Bbody

Cparams

Dheaders

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.params instead of req.query

Trying to get query parameters from req.body

In Express, req.query holds the query string parameters from the URL.

2fill in blank

medium

Complete the code to send back the 'age' query parameter as a number.

Express

app.get('/age', (req, res) => {
  const age = Number(req.[1].age);
  res.send(`You are ${age} years old.`);
});

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

Abody

Bparams

Ccookies

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Not converting the query string to a number

Using req.params instead of req.query

Query parameters are accessed via req.query. They are strings by default, so convert to number if needed.

3fill in blank

hard

Fix the error in accessing the 'search' query parameter.

Express

app.get('/search', (req, res) => {
  const term = req.[1].search;
  res.send(`Searching for: ${term}`);
});

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

Aquery

Bparams

Cbody

Dsession

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.params or req.body instead of req.query

Trying to access query parameters from req.session

The search parameter is part of the query string, so it must be accessed via req.query.

4fill in blank

hard

Fill both blanks to create a response showing 'category' and 'page' from query strings.

Express

app.get('/items', (req, res) => {
  const category = req.[1].category;
  const page = Number(req.[2].page);
  res.send(`Category: ${category}, Page: ${page}`);
});

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

Aquery

Bparams

Cbody

Dcookies

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing req.params and req.query

Not converting page to a number

Both category and page come from query strings, so use req.query for both.

5fill in blank

hard

Fill all three blanks to create a filtered list using 'type', 'sort', and 'limit' query parameters.

Express

app.get('/filter', (req, res) => {
  const type = req.[1].type;
  const sort = req.[2].sort;
  const limit = Number(req.[3].limit);
  res.send(`Filter: type=${type}, sort=${sort}, limit=${limit}`);
});

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

Aparams

Bquery

Cbody

Dcookies

Attempts:

3 left

💡 Hint

Common Mistakes

Using different request properties for each parameter

Forgetting to convert 'limit' to a number

All these values come from the query string, so use req.query for each.

Practice

1. What does req.query represent in an Express app?

easy

A. An object containing URL query parameters sent after the question mark

B. The body data sent in a POST request

C. The headers of the HTTP request

D. The cookies sent by the client

Solution

1. Step 1: Understand the role of req.query

   req.query holds key-value pairs from the URL query string, which comes after the question mark in a URL.

2. Step 2: Differentiate from other request parts

   Body data is accessed via req.body, headers via req.headers, and cookies via req.cookies. So, req.query is specifically for query parameters.

3. Final Answer:

   An object containing URL query parameters sent after the question mark -> Option A

4. Quick Check:

   req.query = URL query parameters [OK]

Hint: Remember: query = URL after '?' [OK]

Common Mistakes:

• Confusing query parameters with body data
• Thinking req.query holds headers or cookies
• Assuming req.query is a string instead of an object

2. Which of the following is the correct way to access a query parameter named id in Express?

easy

A. req.params.id

B. req.query.id

C. req.body.id

D. req.headers.id

Solution

1. Step 1: Identify where query parameters are stored

   Query parameters are stored in req.query, so to get the value of id, use req.query.id.

2. Step 2: Differentiate from other request properties

   req.params is for route parameters, req.body is for POST data, and req.headers is for HTTP headers.

3. Final Answer:

   req.query.id -> Option B

4. Quick Check:

   Query param 'id' = req.query.id [OK]

Hint: Query params always use req.query.[name] [OK]

Common Mistakes:

• Using req.params for query strings
• Trying to get query data from req.body
• Accessing query params from headers

3. Given this Express route handler, what will be logged if the URL is /search?term=books&page=2?

app.get('/search', (req, res) => {
  console.log(req.query.term);
  console.log(req.query.page);
  res.send('Done');
});

medium

A. term\npage

B. undefined\nundefined

C. books\n2

D. books\nundefined

Solution

1. Step 1: Understand the URL query string

   The URL has query parameters: term=books and page=2. These are accessible via req.query.term and req.query.page.

2. Step 2: Check what is logged

   The code logs req.query.term which is "books" and req.query.page which is "2" (strings).

3. Final Answer:

   books 2 -> Option C

4. Quick Check:

   req.query.term = 'books', req.query.page = '2' [OK]

Hint: Query values come as strings from req.query [OK]

Common Mistakes:

• Expecting numbers instead of strings
• Confusing query params with route params
• Assuming undefined if query exists

4. What is the problem with this Express route handler?

app.get('/items', (req, res) => {
  const page = req.query.page;
  if (page > 0) {
    res.send(`Page number is ${page}`);
  } else {
    res.send('Invalid page');
  }
});

medium

A. res.send cannot be called inside an if statement

B. req.query.page is undefined, causing a crash

C. The route should use req.params instead of req.query

D. req.query.page is a string, so numeric comparison may fail

Solution

1. Step 1: Identify the type of req.query.page

   Query parameters are strings by default, so req.query.page is a string, e.g., "1".

2. Step 2: Understand comparison behavior

   Comparing a string with a number using > can lead to unexpected results because string comparison is lexicographic. The code should convert page to a number first.

3. Final Answer:

   req.query.page is a string, so numeric comparison may fail -> Option D

4. Quick Check:

   Convert query strings to numbers before numeric checks [OK]

Hint: Convert query strings to numbers before numeric comparisons [OK]

Common Mistakes:

• Not converting query params to numbers
• Assuming req.query.page is a number
• Using req.params instead of req.query incorrectly

5. You want to create an Express route that reads optional query parameters sort and limit. If limit is missing or not a positive number, it should default to 10. Which code snippet correctly implements this behavior?

hard

A. app.get('/data', (req, res) => {
const sort = req.query.sort || 'asc';
const limit = Number(req.query.limit) > 0 ? Number(req.query.limit) : 10;
res.send(`Sort: ${sort}, Limit: ${limit}`);
});

B. app.get('/data', (req, res) => {
const sort = req.query.sort;
const limit = req.query.limit || 10;
res.send(`Sort: ${sort}, Limit: ${limit}`);
});

C. app.get('/data', (req, res) => {
const sort = req.query.sort ?? 'desc';
const limit = parseInt(req.query.limit) || 10;
res.send(`Sort: ${sort}, Limit: ${limit}`);
});

D. app.get('/data', (req, res) => {
const sort = req.query.sort || 'desc';
const limit = req.query.limit > '0' ? req.query.limit : 10;
res.send(`Sort: ${sort}, Limit: ${limit}`);
});

Solution

1. Step 1: Default sort parameter

   Use req.query.sort || 'asc' to default falsy/missing values to 'asc'.

2. Step 2: Validate limit as positive number

   Number(req.query.limit) > 0 ? Number(req.query.limit) : 10 properly converts, checks positivity (>0), and defaults for missing/undefined/NaN/zero/negative.

3. Step 3: Why others fail

   B: No sort default; limit || 10 accepts invalid like '-1'. C: parseInt(req.query.limit) || 10 accepts negatives ('-1' is truthy). D: req.query.limit > '0' does string comparison, accepts invalid like 'a' ("a" > "0").

4. Final Answer:

   Number(req.query.limit) > 0 ? Number(req.query.limit) : 10 -> Option A

5. Quick Check:

   Convert and validate query params before use [OK]

Hint: Always convert and validate query params before use [OK]

Common Mistakes:

• Not converting query params to numbers
• Using || default with parseInt causing wrong defaults
• Comparing strings directly to numbers