function noDupes (arr) { var dict = {}; var output = []; for (var i = 0; i < arr.length; i++) { if (!dict[arr[i]]) { dict[arr[i]] = 1; } else { dict[arr[i]]++; } } for (var key in dict) { if (dict[key] === 1) { output.push(key); } } return output; } console.log(noDupes([1,3,3,2,4]));