How to unambiguously determine the time zone of a site visitor?

Question

Time Zones

I am working on a project where it will be critical to take into account the time zones of visitors.
How can you uniquely identify them? Ask to specify your city through a special widget or calculate dynamically using JS?

Answer 1

var offset = new Date().getTimezoneOffset();
console.log(offset);

dock and check

where it is critical

it is definitely better to ask for confirmation even after the determination.