Check If a Value Is an Array in JavaScript or Node.js

In some situations you want to check if a given value is an array (or something else). This may be a required check in your code when allowing single items or an array of items as a method argument.

This tutorial walks you through the pitfalls of using typeof and shows you how to properly detect whether a value is an array!

Node.js Series Overview

  1. String Replace All Appearances
  2. Remove All Whitespace From a String in JavaScript
  3. Generate a Random ID or String in Node.js or JavaScript
  4. Remove Extra Spaces From a String in JavaScript or Node.js
  5. Remove Numbers From a String in JavaScript or Node.js
  6. Get the Part Before a Character in a String in JavaScript or Node.js
  7. Get the Part After a Character in a String in JavaScript or Node.js
  8. How to Check if a Value is a String in JavaScript or Node.js
  9. Check If a String Includes All Strings in JavaScript/Node.js/TypeScript
  10. Check if a Value is a String in JavaScript and Node.js
  11. Limit and Truncate a String to a Given Length in JavaScript and Node.js
  12. Split a String into a List of Characters in JavaScript and Node.js
  13. How to Generage a UUID in Node.js
  14. Reverse a String in JavaScript or Node.js
  15. Split a String into a List of Lines in JavaScript or Node.js
  16. Split a String into a List of Words in JavaScript or Node.js
  17. Detect if a String is in camelCase Format in Javascript or Node.js
  18. Check If a String Is in Lowercase in JavaScript or Node.js
  19. Check If a String is in Uppercase in JavaScript or Node.js
  20. Get the Part After First Occurrence in a String in JavaScript or Node.js
  21. Get the Part Before First Occurrence in a String in JavaScript or Node.js
  22. Get the Part Before Last Occurrence in a String in JavaScript or Node.js
  23. Get the Part After Last Occurrence in a String in JavaScript or Node.js
  24. How to Count Words in a File
  25. How to Shuffle the Characters of a String in JavaScript or Node.js
  26. Append Characters or Words to a String in JavaScript or Node.js (Coming soon)
  27. Check if a String is Empty in JavaScript or Node.js (Coming soon)
  28. Ensure a String Ends with a Given Character in JavaScript or Node.js (Coming soon)
  29. Left-Trim Characters Off a String in JavaScript or Node.js (Coming soon)
  30. Right-Trim Characters Off a String in JavaScript or Node.js (Coming soon)
  31. Lowercase the First Character of a String in JavaScript or Node.js (Coming soon)
  32. Uppercase the First Character of a String in JavaScript or Node.js (Coming soon)
  33. Prepend Characters or Words to a String in JavaScript or Node.js (Coming soon)

Determine Whether a Value is a JavaScript Array

You may have used the typeof operator generally in JavaScript. This operator isn’t useful when checking a value for arrays. The reason: arrays in JavaScript are an “object”.

JavaScript handles arrays as a special object with number-based indexes. That’s the reason you’re able to use an index to access array values like array[index]. You can do the same with objects, like object[key].

Also, JavaScript recommends to not use instanceof Array because it doesn’t work across realms. The instanceof check may not work consistently in the browser.

The recommended (and simplest) way to check if a variable is an array is the static Array.isArray method:

Array.isArray()  
Array.isArray(123)  
Array.isArray({ name: 'Future Studio' })  
// all false

Array.isArray([])  
Array.isArray([1, 2, 3])  
Array.isArray(['🥳', '🤜', '🤛'])  
Array.isArray([ { name: 'Future Studio' } ])  
// all true

Array.isArray works in all modern browsers, Node.js, and Deno. Awesome!


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