XTZ.js

Current Time:
YYYY-MM-DDThh:mm:ss.mmm+0000 

new Intl.DateTimeFormat().resolvedOptions().timeZone;
Current Time Zone: America/XXXX 
String(((new Date()).getTimezoneOffset() / 60)).padStart(2, '0') +
String(((new Date()).getTimezoneOffset() % 60)).padStart(2, '0')
Current Time Offset: -0000

Convert Between Time Zones:







Local ISO+Offset String:

XTZ.toLocalISOString(new Date())

TimeZone-Relative (Local) to Absolute (ISO+Offset) String:

XTZ.fromTimeZone("YYYY-03-14 03:15:69.000", "UTC")
   .toISOString()
//





Absolute (UTC) to TimeZone-Relative (ISO+Offset) String:

XTZ.toTimeZone("YYYY-03-14 03:15:69.000", "UTC")
   .toISOString()
//





Time Zones List

See the Full List of Time Zones on Wikipedia. 
America/New_York    -0500 -0400             (Eastern Time)
America/Denver      -0700 -0600             (Mountain Time)
America/Phoenix     -0700 (No DST)          (Arizona Time)
America/Los_Angeles -0800 -0700             (Pacific Time)
UTC                 Z                       (UTC "Zulu" Time)
Australia/Adelaide  +0930 +1030    (30-min)
Asia/Kathmandu      +0545 (No DST) (45-min)
Asia/Kolkata        +0530 (No DST) (30-min)
Code at github.com/therootcompany/tz.js