Get time and date independent of system time

Question

Well, I’m having trouble getting the date and time in Javascript when the computer, or the system has this incorrect data.

• Official time: 08:35 - 07/14/2016 - Brazilian Time
• Computer time: 23:46 - 12/07/2016

No matter what method I try in Javascript, the time always comes based on the Hora do computador, even if you try getUTCDate(), getTimezoneOffset(), etc....

Is there any way to fix this problem only with Javascript? Or do I really need to base myself on a schedule obtained directly from my server?

Note: It is important that the time is correct because it controls the operation of e-commerce site.

Answer 1

There’s no way to do that.

The problem is not of format or time zone, it is error of the hardware use that provides the time. Javascript only takes what the browser provides. The browser only takes what the operating system provides. The OS only provides what the hardware provides. Only the user can change the time since there is no API in Javascript to change the time of the computer.

The solution is to ask the time for the server, at least the first time to know the correct time you have control. If you need to keep the time updated you can use a formula to pick up the shift of the computer’s time relative to the right time, then take the computer’s time and applying this shift before showing.

Answer 2

I tried to set an example using the ideas suggested by @Maniero, @Luizvieira and @Gustavotinoco

var script = document.createElement("script");
script.type = "text/javascript";
script.src = "http://www.timeapi.org/utc/now.json?callback=setDtServer";

var dtServer = null;
var dtClient = null;

//se preferir pode informar um local especifico: ["pt-BR"]
//ou uma lista de locais esperados: ["pt-BR", "pt-PT", "en-US"]
//caso informe uma lista vazia, ele vai tentar inferir o local pelo sistema.
var locales = [];
var formater = new Intl.DateTimeFormat(locales , {
  //é possivel informar o time-zone usando uma string no formato IANA
  //você pode encontrar a lista completa em:
  // http://www.iana.org/time-zones
  // https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
  //No exemplo abaixo estou usando o Timezone de Fortaleza, que difere um
  //pouco do de Brasília, por não fazer parte do Horário de Verão.
  //novamente o valor default vai refletir o que for informado pelo sistema.
  timeZone: "America/Fortaleza",

  year: "numeric",
  month: "numeric",
  day: "numeric",
  hour: "numeric",
  minute: "numeric",
  second: "numeric",
  timeZoneName: "long"
});

function getData() {
  var diff = dtServer.getTime() - dtClient.getTime();
  var data = new Date();
  data.setTime(data.getTime() + diff);
  return data;
}

function setDtServer(json) {
  dtServer = new Date(json.dateString);  
  dtClient = new Date();
  document.head.removeChild(script);  
}

document.head.appendChild(script);
window.setInterval(function () {
  var data = getData();
  console.log(formater.format(data));
}, 1234);

For more information about Date Internationalization with Javascript: Intl.DateTimeFormat

If you need a Polyfill for Intl: Intl.js intl-locales-supported

Answer 3

const options = {
    timeZone: 'America/Sao_Paulo',
    hour: 'numeric',
    minute: 'numeric'
};
const date = new Intl.DateTimeFormat([], options);
console.log(date.format(new Date()));