// To get an array of letters from 'a' to 'z' in javascript.
let alphabet = 'abcdefghijklmnopqrstuvwxyz'.split('');
const alphabet = "abcdefghijklmnopqrstuvwxyz".split("");
const alphabetUp = toUpperCase("abcdefghijklmnopqrstuvwxyz").split("");
[...Array(10).keys()]//=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]