Edit in JSFiddle

let items = [1, 2, 4, 5, 6];
let index = 2;

const firstArr = items.slice(0, index);
const secondArr = items.slice(index + 1);
let newArray = firstArr.concat(secondArr);
console.log('newArray', newArray); // [ 1, 2, 5, 6 ] => 2nd index item deleted
console.log('original items', items); // [ 1, 2, 4, 5, 6 ] => original unaffected