how do i know timezone from date javascript code example

Example 1: javascript set date to timezone

var d = new Date("2020-04-13T00:00:00.000+08:00"); /* midnight in China on April 13th */
d.toLocaleString('en-US', { timeZone: 'America/New_York' });
//=> "4/12/2020, 12:00:00 PM"
// (midnight in China on April 13th is noon in New York on April 12th)

Example 2: get browser timezone javascript

Intl.DateTimeFormat().resolvedOptions().timeZone