req.params for route parameters in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does req.params contain in this route?

Consider this Express route:

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

What will be the output if a client requests /user/42?

Express

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

A {"user":"42"}

B {"params":"42"}

C {}

D {"id":"42"}

💡 Hint

Look at how the route defines the parameter name after the colon.

The req.params object contains key-value pairs where keys are the names defined in the route path. Here, :id means req.params will have a key id with the value from the URL.

📝 Syntax

intermediate

Which route correctly captures two parameters in req.params?

You want to capture both category and itemId from the URL. Which route definition is correct?

A app.get('/shop/:category/:itemId', (req, res) => { res.send(req.params); });

B app.get('/shop/:category,itemId', (req, res) => { res.send(req.params); });

C app.get('/shop/:category&:itemId', (req, res) => { res.send(req.params); });

D app.get('/shop/:category?/:itemId?', (req, res) => { res.send(req.params); });

💡 Hint

Parameters are separated by slashes, not commas or ampersands.

Express route parameters are defined by prefixing names with a colon and separating them by slashes. Option A correctly uses /:category/:itemId.

🔧 Debug

advanced

Why does req.params not contain expected values?

Given this code:

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

What happens when a client requests /post/123?

Express

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

A The response is undefined because req.params.post does not exist.

B The response is '123' as expected.

C The server throws a SyntaxError.

D The response is an empty object {}.

💡 Hint

Check the exact parameter name used in the route and in the code.

The route defines the parameter as postId, but the code tries to access req.params.post. Since post is not defined, it returns undefined.

❓ state_output

advanced

What is the value of req.params for this route and URL?

Route:

app.get('/files/:fileName.:ext', (req, res) => { res.send(req.params); });

URL requested: /files/report.pdf
What does req.params contain?

Express

app.get('/files/:fileName.:ext', (req, res) => { res.send(req.params); });

A {"fileName":"report","ext":".pdf"}

B {"fileName":"report.pdf"}

C {"fileName":"report","ext":"pdf"}

D {}

💡 Hint

Express supports dot-separated parameters in routes.

The route uses :fileName.:ext to capture the file name and extension separately. For /files/report.pdf, fileName is 'report' and ext is 'pdf'.

🧠 Conceptual

expert

Which statement about req.params is true?

Choose the correct statement about req.params in Express routes.

A <code>req.params</code> contains key-value pairs for all URL query parameters.

B <code>req.params</code> only contains parameters defined in the route path with colons.

C <code>req.params</code> is always an empty object unless middleware is used.

D <code>req.params</code> merges route parameters and body parameters automatically.

💡 Hint

Think about how Express separates route parameters from query and body data.

req.params holds only the parameters defined in the route path using colon syntax. Query parameters are in req.query, and body data is in req.body.