GET route handling in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing the GET route?

Consider this Express GET route handler:

app.get('/hello', (req, res) => {
  res.send('Hello World!');
});

What will the client receive when requesting /hello?

Express

app.get('/hello', (req, res) => {
  res.send('Hello World!');
});

A The client receives an empty response with status 200.

B The client receives a JSON object { message: 'Hello World!' }.

C The client receives a 404 Not Found error.

D The client receives the text 'Hello World!' as the response body.

💡 Hint

Look at what res.send does with a string argument.

The res.send method sends the string as the response body with status 200 by default.

📝 Syntax

intermediate

Which option correctly defines a GET route with a URL parameter?

Which of the following Express GET route definitions correctly captures a URL parameter named id?

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

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

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

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

💡 Hint

URL parameters use a colon : before the name.

Option B uses /:id which correctly defines a required URL parameter named id.

Option B treats 'id' as a literal path segment, not a parameter.

Option B uses invalid syntax with angle brackets.

Option B defines an optional parameter with ?, which is valid but changes the route behavior.

🔧 Debug

advanced

Why does this GET route handler cause an error?

Examine this Express GET route handler:

app.get('/data', (req, res) => {
  const data = fetchData();
  res.send(data);
});

Assuming fetchData is an async function returning a Promise, why does this code cause an error or unexpected behavior?

Express

app.get('/data', (req, res) => {
  const data = fetchData();
  res.send(data);
});

A Because res.send cannot be called inside a GET route handler.

B Because fetchData is not defined, causing a ReferenceError.

C Because fetchData returns a Promise, res.send sends the Promise object instead of the resolved data.

D Because the route path '/data' is invalid syntax.

💡 Hint

Think about what happens when you call an async function without awaiting it.

Since fetchData returns a Promise, calling it without await means data is a Promise object. Sending this Promise directly sends the object, not the resolved value.

❓ state_output

advanced

What is the response when accessing this GET route multiple times?

Consider this Express code:

let count = 0;
app.get('/count', (req, res) => {
  count += 1;
  res.send(`Count is ${count}`);
});

What will the client see when requesting /count three times in a row?

Express

let count = 0;
app.get('/count', (req, res) => {
  count += 1;
  res.send(`Count is ${count}`);
});

A The client sees 'Count is 1', then 'Count is 2', then 'Count is 3' on each request.

B The client sees 'Count is undefined' because count is not initialized.

C The client sees 'Count is 0' on the first request and errors on the next.

D The client always sees 'Count is 1' on every request.

💡 Hint

Think about how the variable count changes with each request.

The variable count is stored in the server's memory and increments by 1 on each request, so the response reflects the updated count.

🧠 Conceptual

expert

Which statement about Express GET route matching is true?

Given these routes:

app.get('/item/new', handler2);
app.get('/item/:id', handler1);

Which statement correctly describes how Express matches requests?

A A request to '/item/new' matches handler2 because exact routes have priority over parameter routes.

B A request to '/item/new' matches handler1 because parameter routes match before exact routes.

C A request to '/item/123' matches handler2 because it is defined second.

D A request to '/item/new' causes an error because routes conflict.

💡 Hint

Think about route specificity and matching order in Express.

Express matches routes in order and prefers exact string matches over parameter matches when both could match the same path.

Practice

1. What does the app.get() method do in an Express app?

easy

A. Starts the Express server and listens on a port

B. Defines a route to handle GET requests at a specific URL

C. Sends a POST request to a server

D. Deletes a route from the Express app

Solution

1. Step 1: Understand the purpose of app.get()

   The app.get() method is used to define a route that listens for GET requests on a given URL path.

2. Step 2: Compare with other methods

   Other methods like app.post() handle POST requests, and app.listen() starts the server, so they do not define GET routes.

3. Final Answer:

   Defines a route to handle GET requests at a specific URL -> Option B

4. Quick Check:

   app.get() defines GET routes [OK]

Hint: app.get() always sets up a GET route handler [OK]

Common Mistakes:

• Confusing app.get() with app.listen()
• Thinking app.get() sends requests instead of handling them
• Mixing GET with POST methods

2. Which of the following is the correct syntax to create a GET route for the path /hello that sends "Hello World" as a response?

easy

A. app.get('/hello', (req, res) => { res.send('Hello World'); });

B. app.get('/hello', (res, req) => { res.send('Hello World'); });

C. app.get('/hello', (req, res) => { res.write('Hello World'); });

D. app.get('/hello', (req, res) => { res.sendHello('Hello World'); });

Solution

1. Step 1: Check parameter order in callback

   The callback function parameters must be req first, then res. app.get('/hello', (res, req) => { res.send('Hello World'); }); reverses them, which is incorrect.

2. Step 2: Verify response method usage

   The correct method to send a response string is res.send(). app.get('/hello', (req, res) => { res.write('Hello World'); }); uses res.write() which is not standard in Express, and app.get('/hello', (req, res) => { res.sendHello('Hello World'); }); uses a non-existent method res.sendHello().

3. Final Answer:

   app.get('/hello', (req, res) => { res.send('Hello World'); }); -> Option A

4. Quick Check:

   Correct syntax uses req, res and res.send() [OK]

Hint: Use (req, res) and res.send() to respond in GET routes [OK]

Common Mistakes:

• Swapping req and res parameters
• Using res.write() instead of res.send()
• Calling non-existent response methods

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

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

medium

A. User ID is undefined

B. User ID is :id

C. Error: req.params is not defined

D. User ID is 42

Solution

1. Step 1: Understand route parameters

   The route /user/:id captures the part after /user/ as req.params.id.

2. Step 2: Substitute parameter in response

   When visiting /user/42, req.params.id is "42", so the response is "User ID is 42".

3. Final Answer:

   User ID is 42 -> Option D

4. Quick Check:

   Route params fill req.params.id correctly [OK]

Hint: Use req.params to get URL parts in routes [OK]

Common Mistakes:

• Using req.params without defining route parameter
• Expecting literal ':id' in output
• Forgetting to use backticks for template strings

4. Identify the error in this GET route handler:

app.get('/data', (req, res) => {
  res.send('Data received')
  res.send('Another response');
});

medium

A. Missing semicolon after first res.send()

B. Route path should be '/data/' with trailing slash

C. Cannot call res.send() twice in the same request handler

D. req parameter is unused and causes error

Solution

1. Step 1: Check response sending rules

   Express allows sending only one response per request. Calling res.send() twice causes an error.

2. Step 2: Analyze other options

   Missing semicolons do not cause runtime errors here, trailing slash is optional, and unused parameters do not cause errors.

3. Final Answer:

   Cannot call res.send() twice in the same request handler -> Option C

4. Quick Check:

   Only one res.send() per request allowed [OK]

Hint: Send response only once per route handler [OK]

Common Mistakes:

• Calling res.send() multiple times
• Thinking missing semicolons cause errors
• Confusing trailing slash necessity

5. You want to create a GET route /product/:category/:id that responds with a message like "Category: electronics, ID: 123". Which code correctly implements this?

hard

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

B. app.get('/product/:category/:id', (req, res) => { res.send('Category: req.params.category, ID: req.params.id'); });

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

D. app.get('/product/:category/:id', (req, res) => { res.send(`Category: ${req.query.category}, ID: ${req.query.id}`); });

Solution

1. Step 1: Use correct parameter order and template literals

   The callback must have (req, res) and use backticks with ${} to insert variables. app.get('/product/:category/:id', (req, res) => { res.send(`Category: ${req.params.category}, ID: ${req.params.id}`); }); does this correctly.

2. Step 2: Use req.params for URL parameters

   Route parameters are accessed via req.params, not req.query. app.get('/product/:category/:id', (req, res) => { res.send(`Category: ${req.query.category}, ID: ${req.query.id}`); }); incorrectly uses req.query. app.get('/product/:category/:id', (req, res) => { res.send('Category: req.params.category, ID: req.params.id'); }); uses quotes, so variables won't be evaluated. app.get('/product/:category/:id', (res, req) => { res.send(`Category: ${req.params.category}, ID: ${req.params.id}`); }); swaps parameters.

3. Final Answer:

   app.get('/product/:category/:id', (req, res) => { res.send(`Category: ${req.params.category}, ID: ${req.params.id}`); }); -> Option A

4. Quick Check:

   Use req.params and template literals correctly [OK]

Hint: Use req.params and backticks for dynamic route responses [OK]

Common Mistakes:

• Swapping req and res parameters
• Using string quotes instead of template literals
• Using req.query instead of req.params for route params