javascript add no in array 0 index code example

Example 1: javascript push in specific index

arr.splice(index, 0, item);
//explanation:
inserts "item" at the specified "index",
deleting 0 other items before it

Example 2: set element at index javascript array and create new array

const items = [1, 2, 3, 4, 5]

const insert = (arr, index, newItem) => [
  // part of the array before the specified index
  ...arr.slice(0, index),
  // inserted item
  newItem,
  // part of the array after the specified index
  ...arr.slice(index)
]

const result = insert(items, 1, 10)

console.log(result)
// [1, 10, 2, 3, 4, 5]