Why understanding req matters in Express - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the URL path from the request object in Express.

Express

app.get('/', (req, res) => { const path = req.[1]; res.send(path); });

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

Aurl

Bpath

Cbody

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.url instead of req.path

Trying to access req.body for URL info

The req.path property gives the URL path of the request, which is useful to know what route was accessed.

2fill in blank

medium

Complete the code to get a query parameter named 'id' from the request in Express.

Express

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

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

Abody

Bparams

Cquery

Dheaders

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.body for query params

Using req.params which is for route params

The req.query object holds query string parameters from the URL, like '?id=123'.

3fill in blank

hard

Fix the error in accessing a route parameter named 'userId' in Express.

Express

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

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

Aparams

Bquery

Cbody

Dcookies

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.query or req.body for route params

Trying to access req.cookies.userId

Route parameters like ':userId' are accessed via req.params.

4fill in blank

hard

Fill both blanks to correctly read JSON data sent in a POST request body in Express.

Express

app.post('/data', (req, res) => { const data = req.[1]; const name = data.[2]; res.send(`Name is ${name}`); });

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

Abody

Bparams

Cname

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.query or req.params for POST body data

Trying to access req.body without middleware

JSON data sent in POST requests is accessed via req.body. Then you get the property like name.

5fill in blank

hard

Fill all three blanks to create a route that reads a route param, a query param, and a header value in Express.

Express

app.get('/product/:id', (req, res) => { const productId = req.[1].id; const ref = req.[2].ref; const agent = req.[3]['user-agent']; res.send(`Product: ${productId}, Ref: ${ref}, Agent: ${agent}`); });

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

Aparams

Bquery

Cheaders

Dbody

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up params and query

Trying to get headers from body or query

Route params are in req.params, query params in req.query, and headers in req.headers.

Practice

1. In Express, what does the req object represent?

easy

A. Information sent by the user to the server

B. The server's response to the user

C. A database connection

D. A middleware function

Solution

1. Step 1: Understand the role of req in Express

   The req object contains all the information sent by the user to the server, such as URL parameters, query strings, and request body.

2. Step 2: Differentiate req from other objects

   The server's response is handled by res, not req. Database connections and middleware are separate concepts.

3. Final Answer:

   Information sent by the user to the server -> Option A

4. Quick Check:

   req = user info [OK]

Hint: Remember: req = request from user [OK]

Common Mistakes:

• Confusing req with res (response)
• Thinking req is a database connection
• Mixing req with middleware functions

2. Which of the following is the correct way to access URL parameters in Express?

easy

A. req.body.params

B. req.params

C. req.query.params

D. req.url.params

Solution

1. Step 1: Recall how Express stores URL parameters

   Express stores URL parameters in req.params, which holds key-value pairs from the route.

2. Step 2: Check other options for correctness

   req.body holds POST data, req.query holds query strings, and req.url is a string, not an object with params.

3. Final Answer:

   req.params -> Option B

4. Quick Check:

   URL params = req.params [OK]

Hint: URL params are always in req.params [OK]

Common Mistakes:

• Using req.body to get URL params
• Confusing query strings with URL params
• Trying to access params from req.url string

3. What will be logged by this Express route handler?

app.get('/user/:id', (req, res) => {
  console.log(req.query.name);
  res.send('Done');
});
// Request URL: /user/123?name=Alice

medium

A. undefined

B. 123

C. Alice

D. Error

Solution

1. Step 1: Identify what req.query.name accesses

   req.query holds query string parameters from the URL, so req.query.name gets the value of the 'name' query parameter.

2. Step 2: Match the request URL query

   The URL has ?name=Alice, so req.query.name is 'Alice'.

3. Final Answer:

   Alice -> Option C

4. Quick Check:

   Query param 'name' = Alice [OK]

Hint: Query strings are in req.query [OK]

Common Mistakes:

• Confusing req.params with req.query
• Expecting URL param instead of query param
• Assuming req.query is undefined if not in route

4. Identify the error in this Express route handler:

app.post('/submit', (req, res) => {
  const data = req.query.body;
  res.send(data);
});

medium

A. Using req.query instead of req.body to access POST data

B. Missing res.end() after res.send()

C. Route should be app.get, not app.post

D. req.body is not available without middleware

Solution

1. Step 1: Check how POST data is accessed

   POST data is sent in the request body and accessed via req.body, not req.query.

2. Step 2: Identify the mistake in the code

   The code incorrectly tries to get POST data from req.query.body, which is wrong; it should be req.body.

3. Final Answer:

   Using req.query instead of req.body to access POST data -> Option A

4. Quick Check:

   POST data = req.body, not req.query [OK]

Hint: POST data is in req.body, not req.query [OK]

Common Mistakes:

• Accessing POST data from req.query
• Forgetting to use body-parser middleware
• Confusing HTTP methods and data locations

5. You want to create an Express route that responds differently based on a URL parameter type and a query parameter sort. Which code correctly accesses both parameters?

hard

A. app.get('/items/:type', (req, res) => { const t = req.body.type; const s = req.body.sort; res.send(`${t} sorted by ${s}`); });

B. app.get('/items/:type', (req, res) => { const t = req.query.type; const s = req.params.sort; res.send(`${t} sorted by ${s}`); });

C. app.get('/items', (req, res) => { const t = req.params.type; const s = req.query.sort; res.send(`${t} sorted by ${s}`); });

D. app.get('/items/:type', (req, res) => { const t = req.params.type; const s = req.query.sort; res.send(`${t} sorted by ${s}`); });

Solution

1. Step 1: Identify where URL and query parameters are stored

   URL parameters like type are in req.params, and query parameters like sort are in req.query.

2. Step 2: Check each option for correct usage

   app.get('/items/:type', (req, res) => { const t = req.params.type; const s = req.query.sort; res.send(`${t} sorted by ${s}`); }); correctly uses req.params.type and req.query.sort. app.get('/items/:type', (req, res) => { const t = req.query.type; const s = req.params.sort; res.send(`${t} sorted by ${s}`); }); swaps them incorrectly. app.get('/items', (req, res) => { const t = req.params.type; const s = req.query.sort; res.send(`${t} sorted by ${s}`); }); misses the URL param in route. app.get('/items/:type', (req, res) => { const t = req.body.type; const s = req.body.sort; res.send(`${t} sorted by ${s}`); }); wrongly uses req.body which is for POST data.

3. Final Answer:

   req.params.type and req.query.sort -> Option D

4. Quick Check:

   URL param = req.params, query param = req.query [OK]

Hint: URL params in req.params, query params in req.query [OK]

Common Mistakes:

• Swapping req.params and req.query
• Missing URL param in route path
• Using req.body for GET parameters