findMostRepeatValues

findMostRepeatValues.js

const groupSame = (acc, el) => {
    acc[el] 
      ? acc[el]++
      : acc[el] = 1
    return acc
}
const countDuplicate = (list) => list.reduce(groupSame, {})

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

const findMostRepeat = (el) => groupMostRepeat(countDuplicate([...el]))

console.log(findMostRepeat('Aliquamineratdui.Maurispellentesqueleoatvelitfaucibustinciduntnonideros.')) // i
console.log(findMostRepeat('Lorempsumdolorstamet,consecteturadipiscingelit.')) // t