Validating route params and query in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the route parameter 'id' in Express.

Express

app.get('/user/:id', (req, res) => {
  const userId = req.params.[1];
  res.send(`User ID is ${userId}`);
});

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

Abody

Bquery

Cid

Dparam

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.query instead of req.params for route parameters.

Trying to access req.param instead of req.params.

Route parameters in Express are accessed via req.params using the parameter name, here 'id'.

2fill in blank

medium

Complete the code to access the query parameter 'search' in Express.

Express

app.get('/items', (req, res) => {
  const searchTerm = req.[1].search;
  res.send(`Search term is ${searchTerm}`);
});

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

Aquery

Bparams

Cbody

Dheaders

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.params instead of req.query for query parameters.

Trying to access query parameters from req.body.

Query parameters are accessed via req.query in Express.

3fill in blank

hard

Fix the error in validating that the 'id' route parameter is a number.

Express

app.get('/product/:id', (req, res) => {
  const id = req.params.[1];
  if (isNaN(id)) {
    return res.status(400).send('Invalid ID');
  }
  res.send(`Product ID is ${id}`);
});

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

Aparams

BproductId

Cquery

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong parameter name that does not exist in the route.

Trying to get the parameter from req.query instead of req.params.

The route parameter name is 'id', so use req.params.id to get it.

4fill in blank

hard

Fill both blanks to validate that the 'page' query parameter is a positive integer.

Express

app.get('/list', (req, res) => {
  const page = parseInt(req.[1].[2], 10);
  if (isNaN(page) || page < 1) {
    return res.status(400).send('Invalid page number');
  }
  res.send(`Page number is ${page}`);
});

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

Aquery

Bparams

Cpage

Dbody

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.params instead of req.query for query parameters.

Using a wrong parameter name.

Query parameters are in req.query, and the parameter name is 'page'.

5fill in blank

hard

Fill all three blanks to validate that the 'userId' route param is numeric and 'sort' query param is either 'asc' or 'desc'.

Express

app.get('/users/:userId', (req, res) => {
  const userId = req.params.[1];
  const sort = req.query.[2];
  if (isNaN(userId)) {
    return res.status(400).send('Invalid user ID');
  }
  if (sort !== 'asc' && sort !== [3]) {
    return res.status(400).send('Invalid sort order');
  }
  res.send(`User ID: ${userId}, Sort: ${sort}`);
});

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

AuserId

Bsort

C'desc'

D'asc'

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up route params and query params.

Not checking both allowed sort values.

Using quotes incorrectly around string values.

Use req.params.userId for the route param, req.query.sort for the query param, and check if sort equals 'asc' or 'desc'.

Practice

1. What is the main reason to validate route parameters and query strings in an Express app?

easy

A. To automatically generate HTML pages

B. To speed up the server response time

C. To ensure the data is correct and prevent errors or security issues

D. To change the URL structure dynamically

Solution

1. Step 1: Understand the role of validation

   Validation checks if the data coming from the user is correct and safe to use.

2. Step 2: Identify the benefits of validation

   It prevents errors in the app and protects against malicious input that could cause security problems.

3. Final Answer:

   To ensure the data is correct and prevent errors or security issues -> Option C

4. Quick Check:

   Validation = prevent errors and security risks [OK]

Hint: Validation protects your app from bad or harmful input [OK]

Common Mistakes:

• Thinking validation speeds up the server
• Confusing validation with UI rendering
• Believing validation changes URLs automatically

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

easy

A. req.route.id

B. req.query.id

C. req.body.id

D. req.params.id

Solution

1. Step 1: Recall Express request object properties

   Route parameters are accessed via req.params.

2. Step 2: Match the parameter name

   To get the id parameter, use req.params.id.

3. Final Answer:

   req.params.id -> Option D

4. Quick Check:

   Route params = req.params [OK]

Hint: Route params are always in req.params, not req.query [OK]

Common Mistakes:

• Using req.query for route params
• Trying to get params from req.body without POST data
• Using req.route which is not for params

3. Consider this Express route handler:

app.get('/user/:id', (req, res) => {
  const id = req.params.id;
  if (!/^\d+$/.test(id)) {
    return res.status(400).send('Invalid ID');
  }
  res.send(`User ID is ${id}`);
});

What will be the response if the URL is /user/abc123?

medium

A. User ID is abc123

B. Invalid ID

C. 404 Not Found

D. 500 Internal Server Error

Solution

1. Step 1: Understand the regex validation

   The regex ^\d+$ matches only digits from start to end.

2. Step 2: Check the input against regex

   The input abc123 contains letters, so it fails the test.

3. Step 3: Identify the response on failure

   The code returns status 400 with message 'Invalid ID' when validation fails.

4. Final Answer:

   Invalid ID -> Option B

5. Quick Check:

   Non-digit ID triggers 400 error [OK]

Hint: Regex test fails non-digit IDs, returns 400 error [OK]

Common Mistakes:

• Assuming letters pass the digit-only regex
• Expecting 404 instead of 400 error
• Thinking it returns the ID even if invalid

4. Given this Express route:

app.get('/search', (req, res) => {
  const { term } = req.query;
  if (!term || term.length < 3) {
    res.status(400).send('Search term too short');
  }
  res.send(`Searching for ${term}`);
});

What is the bug in this code?

medium

A. It does not return after sending 400 response, causing headers error

B. It does not check if term is a string

C. It uses req.params instead of req.query

D. It should use POST method instead of GET

Solution

1. Step 1: Analyze the validation logic

   If term is missing or too short, it sends a 400 response.

2. Step 2: Check flow after sending response

   There is no return after res.status(400).send(), so code continues and tries to send another response.

3. Step 3: Identify the error caused

   Sending two responses causes an error about headers already sent.

4. Final Answer:

   It does not return after sending 400 response, causing headers error -> Option A

5. Quick Check:

   Always return after sending error response [OK]

Hint: Return immediately after sending error response [OK]

Common Mistakes:

• Missing return after res.send causes crash
• Confusing req.params with req.query
• Thinking GET cannot have query params

5. You want to validate both a route parameter userId (must be a number) and a query parameter active (must be 'true' or 'false') in Express. Which code snippet correctly validates both and returns 400 errors if invalid?

hard

A. app.get('/user/:userId', (req, res) => {
const { userId } = req.params;
const { active } = req.query;
if (!/^\d+$/.test(userId)) {
return res.status(400).send('Invalid userId');
}
if (active !== 'true' && active !== 'false') {
return res.status(400).send('Invalid active flag');
}
res.send(`User ${userId} active: ${active}`);
});

B. app.get('/user/:userId', (req, res) => {
const userId = Number(req.params.userId);
const active = req.query.active === true;
if (!userId) {
res.status(400).send('Invalid userId');
}
if (active !== true && active !== false) {
res.status(400).send('Invalid active flag');
}
res.send(`User ${userId} active: ${active}`);
});

C. app.get('/user/:userId', (req, res) => {
const { userId, active } = req.params;
if (isNaN(userId)) {
return res.status(400).send('Invalid userId');
}
if (active !== 'true' || active !== 'false') {
return res.status(400).send('Invalid active flag');
}
res.send(`User ${userId} active: ${active}`);
});

D. app.get('/user/:userId', (req, res) => {
const userId = req.params.userId;
const active = req.query.active;
if (typeof userId !== 'number') {
return res.status(400).send('Invalid userId');
}
if (active !== 'true' && active !== 'false') {
return res.status(400).send('Invalid active flag');
}
res.send(`User ${userId} active: ${active}`);
});

Solution

1. Step 1: Validate userId as digits string

   uses regex ^\d+$ on req.params.userId, correctly checking it is numeric string.

2. Step 2: Validate active query param as 'true' or 'false'

   checks active equals 'true' or 'false' strings, returning 400 if not.

3. Step 3: Confirm proper returns after errors

   uses return after sending 400 responses, preventing multiple sends.

4. Final Answer:

   Correctly validates both parameters and returns errors properly -> Option A

5. Quick Check:

   Regex + strict string checks + return after error = correct [OK]

Hint: Use regex for numbers and strict string checks for query params [OK]

Common Mistakes:

• Not returning after res.status(400).send
• Checking query params in req.params
• Using loose type checks instead of strict string comparison