Route parameters in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a route that captures a user ID parameter.

Express

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

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

A:id

B?id

C*id

D#id

Attempts:

3 left

💡 Hint

Common Mistakes

Using *id or ?id instead of :id

Forgetting the colon before the parameter name

The colon : before id defines a route parameter in Express.

2fill in blank

medium

Complete the code to access the route parameter named 'postId'.

Express

app.get('/post/:postId', (req, res) => {
  const postId = req.params.[1];
  res.send(`Post ID: ${postId}`);
});

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

Aid

Bparam

CpostId

Dpost

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different parameter name than defined in the route

Trying to access req.params.id when the parameter is named postId

You access the route parameter by its exact name, here postId.

3fill in blank

hard

Fix the error in the route to correctly capture the 'category' parameter.

Express

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

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

Acategory

B:category

C*category

D?category

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the colon before the parameter name

Using wildcard or optional parameter syntax incorrectly

The route parameter must start with a colon (:), so use ':category'.

4fill in blank

hard

Fill both blanks to define a route with two parameters and access them.

Express

app.get('/[1]/:[2]', (req, res) => {
  res.send(`Category: ${req.params.category}, ID: ${req.params.id}`);
});

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

Acategory

Bid

Cuser

Dpost

Attempts:

3 left

💡 Hint

Common Mistakes

Using parameter syntax for the first segment

Mixing up parameter names

The route path should be '/category/:id' to capture both parameters correctly.

5fill in blank

hard

Fill all three blanks to create a route with nested parameters and access them.

Express

app.get('/[1]/:[2]/[3]/:commentId', (req, res) => {
  res.send(`Post: ${req.params.postId}, Comment: ${req.params.commentId}`);
});

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

Aposts

BpostId

Ccomments

Dcomment

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular instead of plural fixed segments

Forgetting the colon before parameter names

The route path should be '/posts/:postId/comments/:commentId' to capture both post and comment IDs.

Practice

1. What does req.params represent in an Express route handler?

easy

A. An object containing route parameter values from the URL

B. A function to send responses to the client

C. A middleware to parse JSON bodies

D. A method to define static file paths

Solution

1. Step 1: Understand route parameters

   Route parameters are parts of the URL defined with a colon, like /user/:id.

2. Step 2: Accessing parameters in Express

   Express stores these dynamic values in req.params as an object with keys matching parameter names.

3. Final Answer:

   An object containing route parameter values from the URL -> Option A

4. Quick Check:

   req.params = route parameters object [OK]

Hint: Remember: req.params holds URL dynamic parts [OK]

Common Mistakes:

• Confusing req.params with req.body
• Thinking req.params is a function
• Using req.query instead of req.params

2. Which of the following is the correct way to define a route with a parameter named postId in Express?

easy

A. app.get('/post/:postId', (req, res) => { ... })

B. app.get('/post/postId', (req, res) => { ... })

C. app.get('/post/?postId', (req, res) => { ... })

D. app.get('/post/*postId', (req, res) => { ... })

Solution

1. Step 1: Syntax for route parameters

   Express uses a colon : before the parameter name to mark it as dynamic.

2. Step 2: Check each option

   app.get('/post/:postId', (req, res) => { ... }) uses /:postId correctly. Options A, B, and D use incorrect syntax for parameters.

3. Final Answer:

   app.get('/post/:postId', (req, res) => { ... }) -> Option A

4. Quick Check:

   Colon before param name = correct route param syntax [OK]

Hint: Use colon before param name in route path [OK]

Common Mistakes:

• Omitting the colon before parameter name
• Using query syntax instead of route params
• Using wildcard * incorrectly for parameters

3. What will be the output of the following Express route handler when a GET request is made to /user/42?

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

medium

A. User ID is undefined

B. User ID is 42

C. User ID is :id

D. Error: Cannot read property 'id' of undefined

Solution

1. Step 1: Identify the route parameter

   The route defines a parameter :id, so req.params.id will hold the value from the URL.

2. Step 2: Check the request URL and response

   The URL /user/42 sets id to '42', so the response sends 'User ID is 42'.

3. Final Answer:

   User ID is 42 -> Option B

4. Quick Check:

   req.params.id = '42' from URL [OK]

Hint: Route param value replaces :id in req.params [OK]

Common Mistakes:

• Expecting req.params to be undefined
• Using req.query instead of req.params
• Forgetting to use backticks for template literals

4. Consider this Express route:

app.get('/product/:productId', (req, res) => {
  const id = req.params.product;
  res.send(`Product ID: ${id}`);
});

What is the problem with this code?

medium

A. req.params is not accessible in GET routes

B. The route path is missing a colon before productId

C. res.send cannot send strings

D. The route parameter name and req.params key do not match

Solution

1. Step 1: Check route parameter name

   The route defines parameter productId, so req.params will have a key named productId.

2. Step 2: Check usage of req.params

   The code uses req.params.product, which does not exist, so id will be undefined.

3. Final Answer:

   The route parameter name and req.params key do not match -> Option D

4. Quick Check:

   Param name mismatch causes undefined value [OK]

Hint: Match param name exactly in req.params key [OK]

Common Mistakes:

• Using wrong key name from req.params
• Forgetting colon in route path
• Assuming req.params is always empty

5. You want to create an Express route that handles URLs like /order/123/item/456 to get both orderId and itemId. Which route definition and parameter access is correct?

hard

A. app.get('/order/:order/item/:item', (req, res) => { res.send(`Order: ${req.params.orderId}, Item: ${req.params.itemId}`); })

B. app.get('/order/:orderId/item/:itemId', (req, res) => { res.send(`Order: ${req.params.item}, Item: ${req.params.order}`); })

C. app.get('/order/:orderId/item/:itemId', (req, res) => { res.send(`Order: ${req.params.orderId}, Item: ${req.params.itemId}`); })

D. app.get('/order/:orderId/item/:itemId', (req, res) => { res.send(`Order: ${req.query.orderId}, Item: ${req.query.itemId}`); })

Solution

1. Step 1: Define route with two parameters

   The route must have :orderId and :itemId to capture both values from the URL.

2. Step 2: Access parameters correctly

   Use req.params.orderId and req.params.itemId to get the values inside the handler.

3. Final Answer:

   app.get('/order/:orderId/item/:itemId', (req, res) => { res.send(`Order: ${req.params.orderId}, Item: ${req.params.itemId}`); }) -> Option C

4. Quick Check:

   Route params and req.params keys must match [OK]

Hint: Use matching param names in route and req.params [OK]

Common Mistakes:

• Mixing req.params with req.query
• Using wrong parameter names in handler
• Defining route without all needed parameters