Route parameters in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing /user/42?

Consider this Express route:

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

What will the server respond with when a client requests /user/42?

Express

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

A User ID is 42

B Error: Cannot read property 'id' of undefined

C User ID is undefined

D User ID is :id

💡 Hint

Look at how route parameters are accessed via req.params.

The route parameter ':id' captures the part of the URL after '/user/'. It is accessible as req.params.id. So, requesting '/user/42' sets req.params.id to '42'.

📝 Syntax

intermediate

Which route definition correctly captures a product ID?

You want to define a route in Express that captures a product ID from the URL like /product/123. Which of these route definitions is correct?

A app.get('/product/:productId?', (req, res) => { ... });

B app.get('/product/productId', (req, res) => { ... });

C app.get('/product/:productId', (req, res) => { ... });

D app.get('/product/:productId*', (req, res) => { ... });

💡 Hint

Route parameters start with a colon and match one segment.

Option C correctly uses ':productId' to capture the product ID as a route parameter. Option C treats 'productId' as a literal path segment. Option C makes the parameter optional, which is not required here. Option C uses a wildcard which captures multiple segments, not just one.

🔧 Debug

advanced

Why does this route not capture the ID parameter?

Given this Express route:

app.get('/order/:id', (req, res) => { res.send(`Order ID: ${req.params.orderId}`); });

What will happen when a client requests /order/99?

Express

app.get('/order/:id', (req, res) => { res.send(`Order ID: ${req.params.orderId}`); });

A Order ID: undefined

B Order ID: 99

C Error: Cannot read property 'orderId' of undefined

D 404 Not Found

💡 Hint

Check the name used in the route parameter and the name used in req.params.

The route defines the parameter as ':id', so req.params.id contains the value. But the code tries to access req.params.orderId, which is undefined. So the output shows 'Order ID: undefined'.

❓ state_output

advanced

What is the value of req.params after requesting /blog/2023/07?

Consider this Express route:

app.get('/blog/:year/:month', (req, res) => { res.json(req.params); });

What JSON will the server send when a client requests /blog/2023/07?

Express

app.get('/blog/:year/:month', (req, res) => { res.json(req.params); });

A {}

B {"year":"2023","month":"07"}

C {"month":"07"}

D {"year":"2023/07"}

💡 Hint

Each colon-prefixed segment captures one part of the URL path.

The route has two parameters: ':year' and ':month'. The URL '/blog/2023/07' matches both, so req.params contains both keys with their values.

🧠 Conceptual

expert

Which option correctly explains route parameter behavior with optional segments?

Given this route:

app.get('/archive/:year/:month?', (req, res) => { res.send(req.params); });

Which statement is true about accessing /archive/2022 and /archive/2022/12?

A Accessing /archive/2022 sets req.params to { year: '2022', month: null } and /archive/2022/12 sets req.params to { year: '2022', month: '12' }

B Accessing /archive/2022 causes a 404 error because :month is missing

C Accessing /archive/2022 sets req.params to { year: '2022', month: undefined } and /archive/2022/12 sets req.params to { year: '2022', month: '12' }

D Accessing /archive/2022 sets req.params to { year: '2022' } and /archive/2022/12 sets req.params to { year: '2022', month: '12' }

💡 Hint

The question mark after :month makes it optional.

The question mark means the :month parameter is optional. When omitted, req.params does not include the month key at all. When present, it is included with its value.