Does it mutate 😱

Array.prototype.unshift

Mutates

Description

The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.

Array.prototype.unshift ( [ item1 [ , item2 [ , … ] ] ] )

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

Example

var array1 = [1, 2, 3];

console.log(array1.unshift(4, 5));
// expected output: 5

console.log(array1);
// expected output: Array [4, 5, 1, 2, 3]