Сергей Соколов

const yourXFunction = (async1, async2, async3, someCallback) => {
  let latest; // последнее значение остаётся
  Promise.all([
    async1().then(v => {latest = 1; return v;}),
    async2().then(v => {latest = 2; return v;}),
    async3().then(v => {latest = 3; return v;}),
  ]).then(results => {
    console.log("Last was async" + latest);
    someCallback(results[latest - 1]);
  });
}

const yourXFunction = (async1, async2, async3, someCallback) => {
  let latest; // последнее значение остаётся
  Promise.all([
    wrap(async1).then(v => {latest = 1; return v;}),
    wrap(async2).then(v => {latest = 2; return v;}),
    wrap(async3).then(v => {latest = 3; return v;}),
  ]).then(results => {
    someCallback(results[latest - 1]);
  });
}

const wrap = (f) => new Promise((res, rej) => f(res));
    
const async1 = (cb) => {
    setTimeout(() => {
        cb(1);
    }, 4000);
};
const async2 = (cb) => {
    setTimeout(() => {
        cb(13);
    }, 6000);
};
const async3 = (cb) => {
    setTimeout(() => {
        cb(5);
    }, 3000);
};
const someCallback = (val) => console.log(val);

yourXFunction(async1, async2, async3, someCallback);
// через 6 секунд выведет "13"

// так не сработает:
const response = '{"success":1,"data":"{\"esiaId\":null,\"legalMunicipality\":{\"id\":12,\"name\":\"Энгельс\"},\"factMunicipality\":{\"id\":12,\"name\":\"Энгельс\"},\"is_subscribed\":false,\"subscriptions\":null}"}';

// а вот так всё получится:
const response2 = '{"success":1,"data":"{\\\"esiaId\\\":null,\\\"legalMunicipality\\\":{\\\"id\\\":12,\\\"name\\\":\\\"Энгельс\\\"},\\\"factMunicipality\\\":{\\\"id\\\":12,\\\"name\\\":\\\"Энгельс\\\"},\\\"is_subscribed\\\":false,\\\"subscriptions\\\":null}"}';
console.log(response2);
const parsed = JSON.parse(response2);
const data = JSON.parse(parsed.data);
console.log(data.legalMunicipality.name); // Энгельс

const someObject = {a:'value A'};
const arr1 = [1, 'test', someObject];
const arr2 = [100, 200, 'testing', {a:'value A'}];
const arr3 = [1e3, someObject];
const arrays = [arr1, arr2, arr3];

const dict = new Map();

const addArray = (arr, label) => {
  for(let i=0, len=arr.length; i<len; i++) {
    const key = arr[i];
    if (dict.has(key)) return [key, dict.get(key), label];
    dict.set(key, label);
  }
}

for (let i=0, len = arrays.length; i<len; i++) {
  const check = addArray(arrays[i], `arr${i+1}`);
  if (!check) continue;
  console.log(`Value ${check[0]} found in arrays ${check[1]} and ${check[2]}`);
  break;
}
// Value [object Object] found in arrays arr1 and arr3

Class Names

Class names should normally use the CapWords convention.

The naming convention for functions may be used instead in cases where the interface is documented and used primarily as a callable.

Note that there is a separate convention for builtin names: most builtin names are single words (or two words run together), with the CapWords convention used only for exception names and builtin constants.