path.extname for file extensions in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does path.extname do in Node.js?

path.extname returns the file extension part of a file path as a string, including the dot.

beginner

How does path.extname('index.html') evaluate?

It returns '.html' because that is the extension of the file name.

intermediate

What will path.extname('archive.tar.gz') return?

It returns '.gz' because extname only returns the last extension after the last dot.

intermediate

What does path.extname('folder/.hiddenfile') return?

It returns an empty string '' because the file starts with a dot but has no extension after it.

beginner

Why is path.extname useful when working with files?

It helps you find out the type of a file by its extension, so you can decide how to handle or process it.

What does path.extname('photo.jpeg') return?

A 'photo'

B '.jpeg'

C '.photo'

D '' (empty string)

path.extname returns the extension including the dot, so it returns '.jpeg'.

If a file name is '.env', what does path.extname('.env') return?

A null

B '.env'

C '.env' without dot

D '' (empty string)

Files starting with a dot but no extension after it return an empty string.

Which part does path.extname return from 'archive.tar.gz'?

A '.gz'

B '.tar.gz'

C '.tar'

D 'archive'

It returns only the last extension after the last dot, which is '.gz'.

What will path.extname('folder/file') return if the file has no extension?

A '' (empty string)

B null

C '.folder'

D '.file'

If there is no extension, path.extname returns an empty string.

Why should you use path.extname instead of string methods to get file extensions?

A It deletes the extension from the file name.

B It changes the file extension automatically.

C It handles edge cases like hidden files and multiple dots correctly.

D It only works with .txt files.

path.extname is built to correctly find extensions even with tricky file names.

Explain how path.extname works and give an example of its output.

Think about what part of a file name it extracts.

Describe a situation where path.extname might return an empty string.

Consider files without a dot after the name.

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'