Changes

This version has been rewritten and breaks compatibility with the previous API.

Introduction

server-date makes the server's clock available to the client's web browser in JavaScript.

You can use it when you want to display the current time but don't trust the browser's clock to be accurate or to synchronize events for different users of your web site by syncing them all to the server's clock.

There are two implementations. The simplest one, serverDate.js, gets the time from the server on which the library is hosted by reading the Date HTTP response header. You don't need to make any changes on the server if you use this version but its precision is limited to seconds because that's what's available in the header.

If you want millisecond precision, and your server can process PHP, then you can use the serverDate.js.php version which will give you precision on the order of milliseconds.

Usage

import { getServerDate } from "./serverDate.js";

const { date, offset, uncertainty } = await getServerDate();

console.log(`The server's date is ${date} +/- ${uncertainty} milliseconds.`);

// some time in the future

const serverDate = new Date(Date.now() + offset);

See example.html for a complete example.

References

• Cristian, Flaviu (1989), "Probabilistic clock synchronization", Distributed Computing (Springer) 3 (3): 146–158, DOI:10.1007/BF01784024
• MikeWyatt's answer and Willem Mulder's comment in Sync JS time between multiple devices
• Rob W's answer to How to synchronise a client webpage timer with the server

Copyright

Copyright 2012 David Braun