JSFiddle - React, Tailwind, and code Playground

JavaScript

function findOdd(A) {
let tmp = {};
 A.forEach(x => {  
  tmp[x] ? tmp[x]  += 1 : tmp[x] = 1;  
 });
 for (const i in tmp) {
 if (tmp[i] % 2 == 1) {
 tmp = Number(i);  
 break;
 }}
return tmp;
}


/// решение какого-то слишком умного пидораса
const findOdd = (xs) => xs.reduce((a, b) => a ^ b);