intl.js

const date = new Date()
const formatOptions = {
  hour12: false,
  hour: "2-digit",
  minute: "2-digit",
  second: "2-digit"
}

const dtVolgograd = new Intl.DateTimeFormat("en-US", {
  ...formatOptions,
  timeZone: "Europe/Volgograd"
}).format(date)

const dtMoscow = new Intl.DateTimeFormat("en-US", {
  ...formatOptions,
  timeZone: "Europe/Moscow"
}).format(date)

console.log(dtVolgograd === dtMoscow) // `true` expected