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path.extname

Learn to get the file extension with path.extname.

What is path.extname?

path.extname returns the extension of a path; the dot is included. If there is no extension it returns an empty string.

path.extname('report.pdf');    // '.pdf'
path.extname('archive.tar.gz'); // '.gz'
path.extname('README');         // ''

Here the extension of report.pdf comes back as '.pdf'. With multiple dots, the part after the last dot is taken; that is why 'archive.tar.gz' has the extension '.gz'. It is ideal for branching on file type.

extname examples

extname takes only the part after the last dot. So for double extensions like '.tar.gz' it returns only '.gz'. To get the full package extension you need extra logic.

path.extname('backup.tar.gz');  // '.gz'
path.extname('.gitignore');      // ''

In the first example the last dot is before .gz, so the extension is '.gz'. In the second, .gitignore is a hidden file name; the leading dot does not count as an extension and the result is an empty string. This means you must be careful with hidden files.

Practice Your turn: extension with extname

Start with import path from 'path'. Write const ext = path.extname('file.txt'). Log it with console.log(ext).

Starter code

index.js
// Import the path module
// Get the extension with path.extname, log with console.log

Sample solution

index.js
import path from 'path';
const ext = path.extname('file.txt');
console.log(ext);

Expected output

.txt

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What does path.extname('file.txt') return?

  • 'txt'
  • 'file'
  • '.txt' Correct answer
  • 'file.txt'

Explanation: extname returns the extension with the dot.

2 Fill in the blank: extname

Question 
import path from 'path';
const ext = path.____('file.txt');
console.log(ext);
Answer 
import path from 'path';
const ext = path.extname('file.txt');
console.log(ext);

Explanation: You got the extension with extname.

3 extname behaviours

Term Meaning
extname returns extension
dot included
none empty string

All lessons in Beginner

1 Node.js basics

  1. What is Node.js?
  2. Your first program
  3. ES modules
  4. package.json
  5. CommonJS vs ESM
  6. Summary - Node.js basics

2 Variables

  1. let and const
  2. var and scope
  3. Type inference
  4. Destructuring
  5. Spread and rest
  6. Summary - Variables

3 Data types

  1. Primitive types
  2. Template literals
  3. Number and Math
  4. Symbol
  5. typeof
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. process.argv
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Nullish coalescing
  6. Summary - Operators

6 Strings

  1. String methods
  2. String search
  3. substring and slice
  4. replace and split
  5. padStart and trim
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. switch
  4. Ternary
  5. Optional chaining
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. for...of
  4. for...in
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. push and pop
  4. shift and unshift
  5. splice and slice
  6. Summary - Arrays

11 Array methods

  1. map
  2. filter
  3. reduce
  4. find and some
  5. forEach
  6. Summary - Array methods

12 Objects

  1. Object literal
  2. Property access
  3. Computed properties
  4. Object methods
  5. Object spread
  6. Summary - Objects

13 Functions

  1. Defining functions
  2. Return values
  3. Arrow functions
  4. Default parameters
  5. Rest parameters
  6. Summary - Functions

14 Callbacks

  1. What are callbacks?
  2. Higher-order functions
  3. forEach with callbacks
  4. Error-first callbacks
  5. Callback hell
  6. Summary - Callbacks

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Promises

  1. What are promises?
  2. then and catch
  3. Promise.all
  4. Promise.race
  5. finally
  6. Summary - Promises

17 async/await

  1. async function
  2. await
  3. try/catch
  4. await with Promise.all
  5. Sequential await
  6. Summary - async/await

18 fs module

  1. fs.promises
  2. readFile
  3. writeFile
  4. appendFile
  5. existsSync
  6. Summary - fs module

19 path module

  1. path.join
  2. path.resolve
  3. path.parse
  4. path.dirname and basename
  5. path.extname
  6. Summary - path module

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. fs persistence
  5. Putting it together