Добавить элементы в середину массива, используя сплайс
//we can add elements to middle of array using splice
const strings=['a','b','c','d']
//go the 2nd index,remove 0 elements and then add 'alien' to it
strings.splice(2,0,'alien')
console.log(strings) //["a", "b", "alien", "c", "d"]
//what is the time complexity ???
//worst case is O(n). if we are adding to end of array then O(1)
//in our example we added to the middle of array so O(n/2)=>O(n)
Hurt Hummingbird