function duplicates(arr) { arr.sort((a, b) => a - b) const newArr = [] for (let i = 1; i < arr.length; i++) { if (arr[i] === arr[i - 1]) newArr.push(arr[i]) } return Array.from(new Set(newArr)) }
function duplicates(arr) { let set = new Set(); let newArr=[] arr.forEach(element => { if(set.has(element)&&newArr.indexOf(element)==-1){ newArr.push(element) }else{ set.add(element) } }); return newArr; }
function duplicates(arr) { return [...new Set(arr.filter((item) => { return arr.lastIndexOf(item) !== arr.indexOf(item) }))] } let res = duplicates([1, 2, 4, 4, 3, 3, 1, 5, 3]); console.log(res)