Determine a user's timezone?

Question

Is there a standard way for a web server to be able to determine a user's timezone within a web page? Perhaps from an HTTP header or part of the `user-agent` string?

Answer 1

How to check

If you open the developer tools of your browser and navigate to the "Network" tab (naming in Chrome & Firefox), you will see exactly what request headers are sent when visiting a web-site. You will not find any timezone-related information in any header, including the user agent.

How it's usually done

The most common way to identify the user's local time is using JavaScript. As JavaScript runs in the user's browser, you can make a call with the user's time.

Calculations can be based on the offset to GMT or directly working with the timezone provided by JavaScript.

Complex cases

In modern applications, data has to be reliable across multiple users in multiple timezones. It makes sense to set your server to GMT-0 and save any persistent time-entries accordingly, allowing the front-end to do the work of knowing what that means for the current user.