Does it mutate 😱

Array.prototype.splice

Mutates

Description

The splice() method changes the content of an array by removing existing elements and/or adding new elements.

Array.prototype.splice (start, deleteCount [ , item1 [ , item2 [ , … ] ] ] )

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

Example

var months = ['Jan', 'March', 'April', 'June'];
months.splice(1, 0, 'Feb');
// inserts at 1st index position
console.log(months);
// expected output: Array ['Jan', 'Feb', 'March', 'April', 'June']

months.splice(4, 1, 'May');
// replaces 1 element at 4th index
console.log(months);
// expected output: Array ['Jan', 'Feb', 'March', 'April', 'May']