<select id="test">
    <option value="1" data-some="1">один</option>
    <option value="2" data-some="2">два</option>
    ...
    <option value="100" data-some="100">сто</option>
</select>

showMessage()
function showMessage() {
  alert( 'Всем привет!' )
}

obj = document.getElementById('test');
let a = obj.options[obj.selectedIndex].getAttribute('data-some');

let a = obj[obj.selectedIndex].getAttribute('data-some');

async function factorial(n, label) {
    let result  = 1
    let current = n
    const to    = 1

    while (current > to) {
        console.log(label + ' iteration')
        const res = await Promise.resolve(current)

        result *= res
        current--
    }

    return result
}

;(async () => {
    const result = await Promise.allSettled([
        factorial(5, '[first]'),
        factorial(6, '[second]'),
        factorial(7, '[third]')
    ])

    console.log(result)
})()

function macrotask(value) {
    return new Promise(resolve => setTimeout(() => resolve(value), 0))
}