path.extname for file extensions in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of path.extname for a simple file?

Given the following Node.js code using path.extname, what will be printed to the console?

Node.js

import path from 'path';
console.log(path.extname('photo.jpg'));

A '.jpg'

B '.photo'

C 'photo.jpg'

D ''

💡 Hint

Remember, path.extname returns the extension including the dot.

The path.extname function returns the file extension including the dot. For 'photo.jpg', it returns '.jpg'.

❓ Predict Output

intermediate

What does path.extname return for a file with multiple dots?

What will be the output of this code snippet?

Node.js

import path from 'path';
console.log(path.extname('archive.tar.gz'));

A ''

B '.tar.gz'

C '.tar'

D '.gz'

💡 Hint

The extension is the substring after the last dot.

path.extname returns the substring from the last dot to the end. For 'archive.tar.gz', it returns '.gz'.

❓ Predict Output

advanced

What is the output of path.extname for a hidden file?

Consider this code. What will it print?

Node.js

import path from 'path';
console.log(path.extname('.env'));

A ''

B '.'

C '.env.'

D '.env'

💡 Hint

Hidden files start with a dot but may not have an extension.

Files like '.env' start with a dot but have no extension after that. path.extname returns an empty string.

❓ Predict Output

advanced

What does path.extname return for a directory path ending with a dot?

What will this code output?

Node.js

import path from 'path';
console.log(path.extname('/folder.name/.hiddenfile'));

A '.hiddenfile'

B ''

C '.name'

D '.file'

💡 Hint

The extension is based on the last part of the path, not directories.

The last part is '.hiddenfile' which starts with a dot but has no extension after it, so path.extname returns an empty string.

❓ Predict Output

expert

What is the output of path.extname for a filename with trailing dot?

Analyze this code and choose the correct output:

Node.js

import path from 'path';
console.log(path.extname('filename.'));

A '.filename'

B ''

C '.'

D 'filename.'

💡 Hint

The extension includes the last dot and characters after it, even if empty.

When the filename ends with a dot, path.extname returns the dot as the extension.

Practice

1. What does path.extname('example.txt') return in Node.js?

easy

A. '.txt'

B. 'txt'

C. 'example.txt'

D. '' (empty string)

Solution

1. Step 1: Understand what path.extname does

   The path.extname method extracts the file extension including the dot from a filename string.

2. Step 2: Apply to 'example.txt'

   Since the file name is 'example.txt', the extension is '.txt' including the dot.

3. Final Answer:

   '.txt' -> Option A

4. Quick Check:

   Extension includes dot = '.txt' [OK]

Hint: Remember extname returns extension with dot [OK]

Common Mistakes:

• Forgetting the dot in the extension
• Returning the whole filename
• Returning empty string for files with extension

2. Which of the following is the correct syntax to get the extension of a file named 'photo.jpeg' using Node.js path module?

easy

A. path.extname('photo.jpeg')

B. path.extension('photo.jpeg')

C. path.getExt('photo.jpeg')

D. path.ext('photo.jpeg')

Solution

1. Step 1: Recall the correct method name

   The Node.js path module provides the method extname to get file extensions.

2. Step 2: Check the syntax

   The correct syntax is path.extname('filename'). Other options are invalid method names.

3. Final Answer:

   path.extname('photo.jpeg') -> Option A

4. Quick Check:

   Correct method is extname() [OK]

Hint: Use path.extname() exactly as named [OK]

Common Mistakes:

• Using incorrect method names like extension or ext
• Missing parentheses after method name
• Confusing with other path methods

3. What will be the output of the following code?

const path = require('path');
console.log(path.extname('archive.tar.gz'));

medium

A. '.tar.gz'

B. '' (empty string)

C. 'tar.gz'

D. '.gz'

Solution

1. Step 1: Understand how extname handles multiple dots

   The path.extname method returns the substring from the last dot to the end of the string.

2. Step 2: Apply to 'archive.tar.gz'

   The last dot is before 'gz', so the extension returned is '.gz'.

3. Final Answer:

   '.gz' -> Option D

4. Quick Check:

   Extension is from last dot = '.gz' [OK]

Hint: extname returns from last dot to end [OK]

Common Mistakes:

• Assuming it returns multiple extensions
• Returning empty string for multiple dots
• Including the whole suffix after first dot

4. Identify the error in this code snippet:

const path = require('path');
const ext = path.extname('document');
console.log(ext);

medium

A. It returns 'document' as extension

B. It throws an error because 'document' has no extension

C. It returns an empty string because no extension exists

D. It returns undefined

Solution

1. Step 1: Check the filename for extension

   The filename 'document' has no dot, so no extension exists.

2. Step 2: Understand extname behavior with no extension

   path.extname returns an empty string when no extension is found, not an error or undefined.

3. Final Answer:

   It returns an empty string because no extension exists -> Option C

4. Quick Check:

   No dot means empty string [OK]

Hint: No dot means extname returns empty string [OK]

Common Mistakes:

• Expecting an error for missing extension
• Expecting undefined instead of empty string
• Confusing filename with extension

5. You want to filter an array of filenames to only include '.js' files. Which code snippet correctly uses path.extname to do this?

const path = require('path');
const files = ['app.js', 'index.html', 'script.ts', 'readme'];
const jsFiles = files.filter(???);
console.log(jsFiles);

hard

A. file => path.extname(file) === ''

B. file => path.extname(file) === '.js'

C. file => path.extname(file) === '.JS'

D. file => path.extname(file) === 'js'

Solution

1. Step 1: Understand the filter condition

   We want to keep files whose extension is exactly '.js' including the dot and case-sensitive.

2. Step 2: Use path.extname correctly

   The correct comparison is path.extname(file) === '.js'. Other options either miss the dot, use wrong case, or check for empty extension.

3. Final Answer:

   file => path.extname(file) === '.js' -> Option B

4. Quick Check:

   Filter by exact '.js' extension [OK]

Hint: Compare extname result including dot and case [OK]

Common Mistakes:

• Omitting the dot in extension comparison
• Ignoring case sensitivity
• Filtering by empty string instead of '.js'