Does it mutate 😱

Array.prototype.includes()

No mutation

Description

The includes() method determines whether an array includes a certain element, returning true or false as appropriate.

arr.includes(searchElement)
arr.includes(searchElement, fromIndex)

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes

Example

var array1 = [1, 2, 3];

console.log(array1.includes(2));
// expected output: true

var pets = ['cat', 'dog', 'bat'];

console.log(pets.includes('cat'));
// expected output: true

console.log(pets.includes('at'));
// expected output: false