Encoding and decoding URLs in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of decoding a URL component?

Consider the following Node.js code snippet that decodes a URL component. What will be the output?

Node.js

const encoded = 'Hello%20World%21';
const decoded = decodeURIComponent(encoded);
console.log(decoded);

A Hello World!

B Hello%20World%21

C Hello+World!

D SyntaxError

💡 Hint

decodeURIComponent converts percent-encoded characters back to normal characters.

The string 'Hello%20World%21' is percent-encoded. decodeURIComponent converts '%20' to space and '%21' to '!'.

❓ Predict Output

intermediate

What does encodeURI do with special characters?

What is the output of this Node.js code that uses encodeURI on a URL string?

Node.js

const url = 'https://example.com/a file.html?name=John Doe&age=30';
const encoded = encodeURI(url);
console.log(encoded);

A https%3A%2F%2Fexample.com%2Fa%20file.html%3Fname%3DJohn%20Doe%26age%3D30

B https://example.com/a%20file.html%3Fname%3DJohn%20Doe%26age%3D30

C https://example.com/a%20file.html?name=John%20Doe&age=30

D https://example.com/a file.html?name=John Doe&age=30

💡 Hint

encodeURI encodes spaces but leaves URL special characters like ':' and '?' intact.

encodeURI encodes spaces as '%20' but does not encode characters like ':', '/', '?', '=', '&'.

📝 Syntax

advanced

Which option causes a SyntaxError when decoding a URL component?

Which of the following decodeURIComponent calls will cause a SyntaxError in Node.js?

A decodeURIComponent('%E0%A4%A');

B decodeURIComponent('%20');

C decodeURIComponent('%3F');

D decodeURIComponent('Hello%20World');

💡 Hint

Invalid percent-encoding sequences cause SyntaxError in decodeURIComponent.

Option A has an incomplete percent-encoded sequence '%E0%A4%A' which is invalid and causes SyntaxError.

❓ component_behavior

advanced

How does encodeURIComponent treat reserved URL characters?

Given the string 'name=John&age=30', what will encodeURIComponent produce?

Node.js

const input = 'name=John&age=30';
const output = encodeURIComponent(input);
console.log(output);

A name%3DJohn%26age=30

B name=John&age=30

C name%3DJohn&age%3D30

D name%3DJohn%26age%3D30

💡 Hint

encodeURIComponent encodes all characters except letters, digits, and a few others.

encodeURIComponent encodes '=' as '%3D' and '&' as '%26', so the entire string is encoded.

❓ state_output

expert

What is the final value of 'url' after encoding and decoding?

Consider this Node.js code. What is the final value of the variable 'url' after running all lines?

Node.js

let url = 'https://example.com/search?query=Node.js & encoding';
url = encodeURI(url);
url = decodeURIComponent(url);

A https://example.com/search?query=Node.js%20&%20encoding

B https://example.com/search?query=Node.js & encoding

C https://example.com/search?query=Node.js%20%26%20encoding

D gnidocne & sj.edoN=yreuq?hcraes/moc.elpmaxe//:sptth

💡 Hint

encodeURI encodes spaces as '%20' but leaves '&' intact; decodeURIComponent reverses encoding.

encodeURI encodes spaces as '%20' but leaves '&' as is. decodeURIComponent converts '%20' back to space. So final string matches original.