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

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!

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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!

Mentioned Resources

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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