countDuplicateArrayValues

countDuplicateArrayValues.js

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

const findDuplicate = (el) => groupDuplicate([...el])

console.log(findDuplicate('Aliquam in erat dui. Mauris pellentesque leo at velit faucibus tincidunt non id eros.')) 

/*
{ A: 1,
  l: 5,
  i: 9,
  q: 2,
  u: 7,
  a: 5,
  m: 1,
  ' ': 13,
  n: 6,
  e: 8,
  r: 3,
  t: 6,
  d: 3,
  '.': 2,
  M: 1,
  s: 4,
  p: 1,
  o: 3,
  v: 1,
  f: 1,
  c: 2,
  b: 1 }
*/