Count frequency of array elements js
var arr = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4]
const map = arr.reduce((acc, e) => acc.set(e, (acc.get(e) || 0) + 1), new Map());
console.info([...map.keys()]) // to get unique elements
console.info([...map.values()]) // to get the occurrences
console.info([...map.entries()]) // to get the pairs [element, frequency]