If you need to get an array of alphabetical letters in Javascript then you can use one of the following:
Option 1 – Explicitly define the array first
const alphabet = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"];
Option 2 – Split a string of alphabetical characters
const alphabetArray = "abcdefghijklmnopqrstuvwxyz".split("");
Option 3 – Split a string and UpperCase characters
const alphabetArrayUp = toUpperCase("abcdefghijklmnopqrstuvwxyz").split("");