req.query for query strings in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does req.query contain?

In an Express app, when a client sends a URL like /search?term=book&sort=asc, what will req.query contain?

A {"term": "book", "sort": "asc"}

B ["term", "book", "sort", "asc"]

C "term=book&sort=asc"

D undefined

💡 Hint

Think about how query strings are parsed into key-value pairs.

The req.query object contains the parsed query string parameters as key-value pairs. For the URL /search?term=book&sort=asc, req.query will be { term: 'book', sort: 'asc' }.

📝 Syntax

intermediate

Accessing a query parameter safely

Given the URL /items?category=tools, which code correctly accesses the category query parameter in Express?

Express

app.get('/items', (req, res) => {
  // Access category here
});

A const category = req.params.category;

B const category = req.query.category;

C const category = req.body.category;

D const category = req.query[0];

💡 Hint

Query parameters come from the URL after the question mark.

Query parameters are accessed via req.query. Route parameters use req.params, and POST data uses req.body.

🔧 Debug

advanced

Why is req.query.page undefined?

An Express route expects a query parameter page. The URL is /list?page=2. The code is:

app.get('/list', (req, res) => {
  const page = req.query.page;
  res.send(`Page number is ${page}`);
});

But the response shows Page number is undefined. What is the likely cause?

A The client did not send the query string properly; the URL is missing the question mark.

B The Express app is missing middleware to parse query strings.

C The query parameter name is case-sensitive and should be uppercase.

D The route path is incorrect and does not match the URL.

💡 Hint

Check the URL format carefully.

If the URL does not contain a question mark before query parameters, req.query will be empty. The URL must be /list?page=2, not /listpage=2.

❓ state_output

advanced

What is the output of this Express route?

Consider this Express route:

app.get('/filter', (req, res) => {
  const { type = 'all', limit = 10 } = req.query;
  res.json({ type, limit });
});

What will be the JSON response for the URL /filter?limit=5?

A {"type": "all", "limit": 5}

B {"type": undefined, "limit": 5}

C {"type": "all", "limit": "5"}

D {"type": "all", "limit": 10}

💡 Hint

Remember that query parameters are strings by default.

Query parameters are strings, so limit is the string "5". The default type is used because it was not provided.

🧠 Conceptual

expert

Handling multiple values for the same query key

If a client sends the URL /search?tag=js&tag=node&tag=express, what will req.query.tag contain in Express by default?

A undefined

B ["js", "node", "express"]

C "js"

D "express"

💡 Hint

Express uses a simple parser for query strings by default.

By default, Express's query parser returns the last value for repeated keys. So req.query.tag will be the string "express".