arr = [1,2,3,2,3,3,4]; function itemByFrequency(arr, freq){ filterFrequencies = function(o,n){ o[n] = o[n] || 0; o[n] += 1; if (o[n] == freq) o.result.push(n); return o; }; return arr.reduce(filterFrequencies, {"result":[]}).result; } console.log(itemByFrequency(arr,2));