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Dom Habersack
Dom Habersack

Posted on • Originally published at

🔥 How to check if something is an array in JavaScript

Internally, there is no type called “array” in JavaScript. When used on an array, typeof returns "object" instead.

To check if something is an array, use Array.isArray() instead.

// `typeof` an array returns “object” because JS has no type called “array”.
typeof ['a', 'b', 'c']                     // ⇒ "object"

// The array is treated like this equivalent object.
typeof { 0: 'a', 1: 'b', 2: 'c' }          // ⇒ "object"

// Use `Array.isArray` instead of `typeof` to test if something is an array.
Array.isArray(['a', 'b', 'c'])             // ⇒ true
Array.isArray({ 0: 'a', 1: 'b', 2: 'c' })  // ⇒ false
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Top comments (4)

eliabe45 profile image
Eliabe França

I've always used instaceof

brandonmweaver profile image
Brandon Weaver

This is more readable in my opinion.
[0] instanceof Array; // true

domhabersack profile image
Dom Habersack

That is a decent alternative. It could cause issues when working with multiple frames, because each context has its own Array object:

When working with iframes, Array.isArray() gives you more accurate results. When working with a single context, instanceof is fine.

seyeolajuyin profile image
Seye Olajuyin

I had no idea this exists. Thank you!