URLSearchParams for query strings in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this code using URLSearchParams?

Consider the following Node.js code snippet that uses URLSearchParams. What will be printed to the console?

Node.js

const params = new URLSearchParams('name=alice&age=30&city=NY');
console.log(params.get('age'));

A "NY"

B "alice"

C null

D "30"

💡 Hint

Remember that get returns the value of the given key from the query string.

The get method returns the value associated with the given key. Here, age is "30".

📝 Syntax

intermediate

Which option correctly creates a URLSearchParams object from an object?

You want to create a URLSearchParams instance from this object: { foo: 'bar', count: 5 }. Which code snippet works without error?

A new URLSearchParams([['foo', 'bar'], ['count', '5']])

B new URLSearchParams({ foo: 'bar', count: 5 })

C new URLSearchParams('foo=bar&count=5')

D new URLSearchParams({ foo: 'bar', count: '5' })

💡 Hint

URLSearchParams accepts a string or an iterable of key-value pairs, not a plain object.

Only option A uses an iterable of key-value pairs (array of arrays), which is valid. Options B and D pass plain objects, which cause a TypeError. Option A uses a string, which works but is not from an object.

🔧 Debug

advanced

Why does this code throw a TypeError?

Examine the code below. Why does it throw a TypeError?

Node.js

const params = new URLSearchParams({ key: 'value' });
console.log(params.toString());

A URLSearchParams constructor does not accept plain objects, only strings or iterable key-value pairs

B The toString method is not defined on URLSearchParams instances

C The key 'key' is reserved and cannot be used in URLSearchParams

D The value 'value' must be a number, not a string

💡 Hint

Check the allowed argument types for URLSearchParams constructor.

The constructor expects a string or iterable of pairs. Passing a plain object causes a TypeError.

❓ state_output

advanced

What is the final query string after these operations?

Given the following code, what will params.toString() output?

Node.js

const params = new URLSearchParams('a=1&b=2&c=3');
params.set('b', '20');
params.append('d', '4');
params.delete('a');

A "a=1&b=20&c=3"

B "b=20&c=3&d=4"

C "b=2&c=3&d=4"

D "a=1&b=20&c=3&d=4"

💡 Hint

Remember that set replaces the value, append adds a new value, and delete removes the key.

After deleting 'a', setting 'b' to '20', and appending 'd=4', the query string is 'b=20&c=3&d=4'.

🧠 Conceptual

expert

Which option correctly explains how URLSearchParams handles multiple values for the same key?

If a query string contains multiple values for the same key, how does URLSearchParams behave when using get and getAll methods?

A <code>get</code> returns the last value; <code>getAll</code> returns only the first value

B <code>get</code> returns all values as a comma-separated string; <code>getAll</code> returns the last value

C <code>get</code> returns the first value; <code>getAll</code> returns all values as an array

D <code>get</code> throws an error if multiple values exist; <code>getAll</code> returns all values

💡 Hint

Think about how to retrieve one or all values for a repeated key.

get returns the first value for a key. getAll returns an array of all values for that key.

Practice

1. What does the URLSearchParams class in Node.js primarily help you do?

easy

A. Easily read and modify URL query strings

B. Create HTTP servers

C. Parse JSON data

D. Manage file system paths

Solution

1. Step 1: Understand the purpose of URLSearchParams

   URLSearchParams is designed to work with the query part of URLs, making it easy to read and change parameters.

2. Step 2: Compare with other options

   Creating servers, parsing JSON, or managing file paths are unrelated to URLSearchParams.

3. Final Answer:

   Easily read and modify URL query strings -> Option A

4. Quick Check:

   URLSearchParams = query string helper [OK]

Hint: URLSearchParams = query string helper [OK]

Common Mistakes:

• Confusing URLSearchParams with server or file system modules
• Thinking it parses JSON data
• Assuming it manages entire URLs, not just query strings

2. Which of the following is the correct way to create a URLSearchParams object from a query string in Node.js?

easy

A. const params = new URLSearchParams({name: 'John', age: 30});

B. const params = URLSearchParams('?name=John&age=30');

C. const params = URLSearchParams({name: 'John', age: 30});

D. const params = new URLSearchParams('?name=John&age=30');

Solution

1. Step 1: Check the correct syntax for creating URLSearchParams

   The constructor requires the new keyword and accepts a query string like '?name=John&age=30'.

2. Step 2: Identify incorrect options

   Options without new or passing an object directly without conversion are invalid.

3. Final Answer:

   const params = new URLSearchParams('?name=John&age=30'); -> Option D

4. Quick Check:

   Use new with query string [OK]

Hint: Always use 'new' with URLSearchParams and a query string [OK]

Common Mistakes:

• Omitting the 'new' keyword
• Passing an object directly without converting to string
• Using URLSearchParams as a function, not a constructor

3. What will the following code output?

const params = new URLSearchParams('color=blue&size=medium');
params.set('size', 'large');
console.log(params.toString());

medium

A. color=blue&size=medium

B. color=blue

C. color=blue&size=large

D. size=large&color=blue

Solution

1. Step 1: Understand params.set()

   The set method updates the value of the 'size' parameter from 'medium' to 'large'.

2. Step 2: Check the output of toString()

   The toString() method returns the query string with updated parameters in the order they were added.

3. Final Answer:

   color=blue&size=large -> Option C

4. Quick Check:

   set() updates value, toString() shows updated string [OK]

Hint: set() changes value; toString() shows updated query [OK]

Common Mistakes:

• Assuming set() adds a new parameter without replacing
• Thinking order of parameters changes
• Forgetting to call toString() to see the string

4. Identify the error in this code snippet:

const params = new URLSearchParams('page=1&limit=10');
params.append('page', 2);
console.log(params.get('page'));

medium

A. get() returns only the first 'page' value, ignoring the appended one

B. append() replaces the existing 'page' parameter instead of adding

C. URLSearchParams constructor cannot accept strings

D. append() requires both parameters to be strings

Solution

1. Step 1: Understand append() behavior

   append() adds another 'page' parameter, so now there are two 'page' keys.

2. Step 2: Understand get() behavior

   get() returns the first value for 'page', which is '1', ignoring the appended '2'.

3. Final Answer:

   get() returns only the first 'page' value, ignoring the appended one -> Option A

4. Quick Check:

   get() returns first value when duplicates exist [OK]

Hint: get() returns first value; use getAll() for all [OK]

Common Mistakes:

• Thinking append() replaces existing keys
• Expecting get() to return all values
• Assuming constructor rejects strings

5. You want to build a URL query string from an object { search: 'books', page: 2, filter: '' } but want to exclude empty values. Which code correctly creates the query string using URLSearchParams?

hard

A. const params = new URLSearchParams({ search: 'books', page: '2', filter: '' });
console.log(params.toString());

B. const params = new URLSearchParams();
for (const [key, value] of Object.entries({ search: 'books', page: 2, filter: '' })) {
if (value) params.append(key, value.toString());
}
console.log(params.toString());

C. const params = new URLSearchParams();
Object.entries({ search: 'books', page: 2, filter: '' }).forEach(([k,v]) => params.set(k,v));
console.log(params.toString());

D. const params = new URLSearchParams();
for (const key in { search: 'books', page: 2, filter: '' }) {
params.append(key, '');
}
console.log(params.toString());

Solution

1. Step 1: Understand the goal to exclude empty values

   We want to skip keys with empty strings, so we check if the value is truthy before adding.

2. Step 2: Analyze each option

   const params = new URLSearchParams({ search: 'books', page: '2', filter: '' }); console.log(params.toString()); includes empty 'filter' value. const params = new URLSearchParams(); for (const [key, value] of Object.entries({ search: 'books', page: 2, filter: '' })) { if (value) params.append(key, value.toString()); } console.log(params.toString()); adds only truthy values. const params = new URLSearchParams(); Object.entries({ search: 'books', page: 2, filter: '' }).forEach(([k,v]) => params.set(k,v)); console.log(params.toString()); adds all including empty. const params = new URLSearchParams(); for (const key in { search: 'books', page: 2, filter: '' }) { params.append(key, ''); } console.log(params.toString()); adds empty strings for all keys.

3. Final Answer:

   Option B correctly filters out empty values before appending -> Option B

4. Quick Check:

   Filter empty values before append() [OK]

Hint: Check value truthiness before adding to URLSearchParams [OK]

Common Mistakes:

• Passing object directly without filtering empty values
• Using set() without filtering, adding empty keys
• Appending empty strings for all keys