Array.prototype.toSpliced()

toSpliced(start)
toSpliced(start, deleteCount)
toSpliced(start, deleteCount, item1)
toSpliced(start, deleteCount, item1, item2)
toSpliced(start, deleteCount, item1, item2, /* , */ itemN)

const months = ["Jan", "Mar", "Apr", "May"];

//  1  
const months2 = months.toSpliced(1, 0, "Feb");
console.log(months2); // ["Jan", "Feb", "Mar", "Apr", "May"]

//  2 2  
const months3 = months2.toSpliced(2, 2);
console.log(months3); // ["Jan", "Feb", "May"]

//  1       
const months4 = months3.toSpliced(1, 1, "Feb", "Mar");
console.log(months4); // ["Jan", "Feb", "Mar", "May"]

//    
console.log(months); // ["Jan", "Mar", "Apr", "May"]

const arr = [1, , 3, 4, , 6];
console.log(arr.toSpliced(1, 2)); // [1, 4, undefined, 6]

const arrayLike = {
  length: 3,
  unrelated: "foo",
  0: 5,
  2: 4,
};
console.log(Array.prototype.toSpliced.call(arrayLike, 0, 1, 2, 3));
// [2, 3, undefined, 4]