contest.js

const assignVehicles = (vehicles, drivers) => {
    vehicles = JSON.parse(JSON.stringify(vehicles))
    drivers = JSON.parse(JSON.stringify(drivers))
    vehicles.sort((a, b) => a.year - b.year)
    drivers.sort((a, b) => b.age - a.age)
    // console.log('Sorted:', vehicles, drivers)
    let result = {
        vehicles: {},
        drivers: {}
    }
    vehicles.map((v, i) => {
        let driver = drivers[i] || drivers[drivers.length - 1]
        result.vehicles[v.id] = driver.id
        result.drivers[driver.id] = v.id
    })
    if (vehicles.length < drivers.length) {
        drivers.slice(vehicles.length,).map((v, i) => {
            let vehicle = vehicles[vehicles.length - 1]
            result.drivers[v.id] = vehicle.id
        })
    }
    return result
}

const vehicles = [
    {
        id: '1',
        year: 1,
    },
    {
        id: '2',
        year: 3,
    },
    {
        id: '3',
        year: 10,
    }
]

drivers = [
    {
        id: '1',
        age: 30,

    },
    {
        id: '2',
        age: 24,
    },
    {
        id: '3',
        age: 40,
    },
    {
        id: '4',
        age: 31
    }
]


const test = (a, b) => {
    console.log(a, b);
    let r = assignVehicles(a, b)
    console.log(r)
}

test(vehicles, drivers.slice(0, vehicles.length))
test(vehicles, drivers.slice(0, vehicles.length - 1))
test(vehicles, drivers)