Highest in a string

highest.js

const s = 'abcergsserswsGiogjadSf48ewfu64896'
const listByKey = Array.from(s).reduce((acc, char) => {
	if (!isNaN(char)) return acc

  const letter = char.toLowerCase()
  
  const count = acc[letter] ? acc[letter] + 1 : 1
  
	return {
  	...acc,
    [letter]: count
  }
}, {})

const highest = Object.keys(listByKey).reduce((a, b) => listByKey[a] > listByKey[b] ? a : b)