Does it mutate 😱
Array.prototype.concat
No mutation
Description
The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.
Array.prototype.concat ( [ item1 [ , item2 [ , … ] ] ] )https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/concat
Example
var array1 = ['a', 'b', 'c'];
var array2 = ['d', 'e', 'f'];
console.log(array1.concat(array2));
// expected output: Array ["a", "b", "c", "d", "e", "f"]