[Go Make Things] The Array.prototype.every() method always returns true for an empty array

By rahmat hidayat

Thursday, September 7, 2023

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My friend Nicholas Zakas made an interesting observation on Mastodon this week: the Array.prototype.every() method always returns true for an empty array.

let arr = [];    // Returns true  arr.every(function (item) {  	return false;  });    // Also returns true  arr.every(function (item) {  	return true;  });  

Axel Rauschmayer provided an interesting explanation…

.every() implements universal quantification ("for all", ∀). And that operator is always true for empty sets…

That is also how we understand [for all] intuitively if we use it in natural language: "All humans that live on Venus have blue skin" is true (because no humans live on Venus).

The Vanilla JS Academy is a project-based online JavaScript workshop for beginners. Click here to learn more.

Cheers,
Chris

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