Does getTimezoneOffset change when you move timezones on a mobile browser

When I am in Chicago using a mobile browser, and I get timezone offset of -360, for -6 hours. If I get on a plane and fly to San Fransisco, do I automatically see that adjusted to -480 for -8 hrs, without changing the timezone on the phone? That is does th开发者_如何学JAVAe clock pick up the timezone from the cell tower, and reset it in a way that the javascript engine knows?