airline-tickets.js

// SLC -> AUS -> LAX -> JFK -> SJC

let passes = [
    {depart: 'JFK', arrive: 'SJC'},
    {depart: 'LAX', arrive: 'JFK'},
    {depart: 'AUS', arrive: 'LAX'},
    {depart: 'SLC', arrive: 'AUS'}
];


let departures = [];
let destinations = [];

let start, finish;

passes.forEach(pass => {
    departures.push(pass.depart);
    destinations.push(pass.arrive);

    if(!destinations.includes(pass.depart)) {
        start = pass.depart;
    }

    if(!departures.includes(pass.arrive)) {
        finish = pass.arrive;
    }
});

console.log(`${start} -> ${finish}`);