arr = [1,2,3,2,3,4]; function itemByFrequency(arr, freq){ function countFrequencies(o,n){ o[n] = o[n] || 0; o[n] += 1; return o; } var fr = arr.reduce(countFrequencies, {}); function filterFrequencies(o,n){ if (fr[n]==freq) o.push(n); return o; } return Object.keys(fr).reduce(filterFrequencies, []); } console.log(itemByFrequency(arr,2));