make_route.js

function getRoute (tickets) {
  const route = tickets.pop();
  let i = 0;
  while (i < tickets.length) {
    if (route[0] === tickets[i][1]) {
      route.unshift(tickets[i][0]);
      i = 0;
    } else if (route[route.length - 1] === tickets[i][0]) {
      route.push(tickets[i][1]);
      i = 0;
    } else i++;
  }
  return route.toString();
}

const result = getRoute([["JPN", "PHL"], ["BRA", "UAE"], ["USA", "BRA"], ["UAE", "JPN"]]);

console.log(result)