How to get value from interval?

Question

JavaScript

var promise = new Promise((resolve, reject) => {
        let intervalId = setInterval(function() {
            let damage = getDamage(firstFighter, secondFighter);
            if (damage > 0) {
                console.log(secondFighterHealth + "-" + damage);
                secondFighterHealth -= damage;
            }else{
                console.log('Второй блокировал удар первого!');
            }
            console.log('Second Health: ' + secondFighterHealth);

            damage = getDamage(secondFighter, firstFighter);
            if (damage > 0) {
                console.log(firstFighterHealth + "-" + damage);
                firstFighterHealth -= damage;
            }else{
                console.log('Первый блокировал удар второго!');
            }

            console.log('First Health: ' + firstFighterHealth);

            if(firstFighterHealth <= 0) {
                window.winner = secondFighter;
                clearInterval(intervalId);
                resolve(winner);
            }else if(secondFighterHealth <= 0) {
                window.winner = firstFighter;
                clearInterval(intervalId);
                resolve(winner);
            }
        }, 1000);
    });
    promise.then(
        result => alert('Winner - ' + winner.name)
    )

In the interval, by taking the life of each character, a winner is chosen.
It is necessary to return the object of the winner from the function.
Through promises does not work.

Answer 1

Read the documentation on promises, you have a lot of shit in your code.
Why async in your case, why await? Do you really understand how to use them?
My recommendation is to forget about them for a while and learn how to write working code on pure Promises, and only when you understand everything, you can try to return to async and await.

if (firstFighterHealth <= 0) {
        winner = secondFighter;
        clearInterval(intervalId);
        resolve(winner);
        // console.log(winner.name);
        // return winner;
      } else if (secondFighterHealth <= 0) {

You win either the first player or the second, the third is not given, why else if? Use the normal else

let damage = getDamage(firstFighter, secondFighter);
if (damage > 0) {

Twice similar code, why take damage to a variable, why not write
if (getDamage(firstFighter, secondFighter) > 0)
if (getDamage(secondFighter, firstFighter) > 0)
Why not pass the current damage as the third parameter to the getDamage function, and remove the logic blocking into a common function, it is repeated, you can immediately return new damage
firstFighterHealth = getDamage(firstFighter, secondFighter, firstFighterHealth )
secondFighterHealth = getDamage(secondFighter, firstFighter, secondFighterHealth )
Before the interval, you need to do let firstFighterHealth = secondFighterHealth = 0;