JSFiddle - React, Tailwind, and code Playground

JavaScript

var array1 = [1, 2, 3, 5];
var array2 = [1, 2, 3, 4, 5];

var filteredArray = filter(array1, array2).concat(filter(array2, array1));

function filter(arr1, arr2){
 return arr1.filter(function (el) { return arr2.indexOf(el) < 0; });
}

alert(filteredArray)
// expected output: [4]