function diff(arr1, arr2) { var newArr = arr1.concat(arr2); console.log(newArr); //Outputs [1, 2, 3, 5, 1, 2, 3, 4, 5] var filteredArr = newArr.filter(function(elem, pos) { return newArr.indexOf(elem) === pos; }) console.log(filteredArr); //Outputs [1, 2, 3, 5, 4] } diff([1, 2, 3, 5], [1, 2, 3, 4, 5]);