JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr1 = [1, 2, 5, 9],
    arr2 = [2, 5, 100, 0, 41];

var grouped = arr1.concat(arr2).reduce((acc, next) => {
	acc[next] = (acc[next] || 0) + 1;
  return acc;
}, {});

console.log(Object.keys(grouped).filter(key => grouped[key] == 1).length);