Array.prototype.splice()

const months = ["Jan", "March", "April", "June"];
months.splice(1, 0, "Feb");
// Inserts at index 1
console.log(months);
// Expected output: Array ["Jan", "Feb", "March", "April", "June"]

months.splice(4, 1, "May");
// Replaces 1 element at index 4
console.log(months);
// Expected output: Array ["Jan", "Feb", "March", "April", "May"]

array.splice(start[, deleteCount[, item1[, item2[, ...]]]])

var myFish = ["angel", "clown", "mandarin", "sturgeon"];
var removed = myFish.splice(2, 0, "drum");

// myFish  ["angel", "clown", "drum", "mandarin", "sturgeon"]
// removed  [], 

var myFish = ["angel", "clown", "drum", "mandarin", "sturgeon"];
var removed = myFish.splice(3, 1);

// removed  ["mandarin"]
// myFish  ["angel", "clown", "drum", "sturgeon"]

var myFish = ["angel", "clown", "drum", "sturgeon"];
var removed = myFish.splice(2, 1, "trumpet");

// myFish  ["angel", "clown", "trumpet", "sturgeon"]
// removed  ["drum"]

var myFish = ["angel", "clown", "trumpet", "sturgeon"];
var removed = myFish.splice(0, 2, "parrot", "anemone", "blue");

// myFish  ["parrot", "anemone", "blue", "trumpet", "sturgeon"]
// removed  ["angel", "clown"]

var myFish = ["parrot", "anemone", "blue", "trumpet", "sturgeon"];
var removed = myFish.splice(myFish.length - 3, 2);

// myFish  ["parrot", "anemone", "sturgeon"]
// removed  ["blue", "trumpet"]

var myFish = ["angel", "clown", "mandarin", "sturgeon"];
var removed = myFish.splice(-2, 1);

// myFish  ["angel", "clown", "sturgeon"]
// removed  ["mandarin"]

var myFish = ["angel", "clown", "mandarin", "sturgeon"];
var removed = myFish.splice(2);

// myFish  ["angel", "clown"]
// removed  ["mandarin", "sturgeon"]