https://www.wicurio.com/pkwk/skin/tzCalculation_LocalTimeZone.js

1// White Papers
2// Time Zone Calculation
3// http://www.desisoftsystems.com/white-papers/timeZoneCalculation/
4//
5// Conclusion
6// In the interest of promoting open standards, you are free to use 
7// the source code in this white paper and the code available in this JavaScript source file:
8//
9// http://www.desisoftsystems.com/tzCalculation_LocalTimeZone.js
10//
11// to implement this solution to this world-wide problem.
12//
13function tzCalculation_LocalTimeZone (
14	theDomainForTheCookie,
15	printTheTimeZone)
16{	// Beginning of tzCalculation_LocalTimeZone
17    var rightNow;
18    var rightNow_UTC_MillisecondsSinceTimBegan;
19    var rightNow_Local_MillisecondsSinceTimBegan;
20    var rightNow_MillisecondsDifference;
21    var rightNow_MinutesDifference;
22    var rightNow_timeZoneString;
23    var rightNow_MinutesPart;
24    var rightNow_HoursDifference;
25
26	rightNow = new Date();
27
28	rightNow_UTC_MillisecondsSinceTimBegan = Date.UTC (
29		rightNow.getUTCFullYear (),
30		rightNow.getUTCMonth (),
31		rightNow.getUTCDate (),
32		rightNow.getUTCHours (),
33		rightNow.getUTCMinutes (),
34		rightNow.getUTCSeconds ()
35		);
36	rightNow_Local_MillisecondsSinceTimBegan = Date.UTC (
37		rightNow.getFullYear (),
38		rightNow.getMonth (),
39		rightNow.getDate (),
40		rightNow.getHours (),
41		rightNow.getMinutes (),
42		rightNow.getSeconds ()
43		);
44
45	rightNow_MillisecondsDifference = rightNow_Local_MillisecondsSinceTimBegan - rightNow_UTC_MillisecondsSinceTimBegan;
46
47	rightNow_MinutesDifference = (rightNow_MillisecondsDifference / 1000) / 60;
48
49	if (0 > rightNow_MinutesDifference)
50	{
51		rightNow_timeZoneString = "-";
52	}
53	else
54	{
55		rightNow_timeZoneString = "+";
56	}
57
58	rightNow_MinutesPart = rightNow_MinutesDifference % 60;
59
60	if (rightNow_MinutesPart != 0)
61	{
62		rightNow_MinutesDifference -= rightNow_MinutesPart;
63
64		if (0 > rightNow_MinutesPart)
65		{
66			rightNow_MinutesPart = Math.abs (rightNow_MinutesPart);
67		}
68	}
69
70	if (0 > rightNow_MinutesDifference)
71	{
72		rightNow_MinutesDifference = Math.abs (rightNow_MinutesDifference);
73	}
74
75	rightNow_HoursDifference = rightNow_MinutesDifference / 60;
76
77	if (10 > rightNow_HoursDifference)
78	{
79		rightNow_timeZoneString = rightNow_timeZoneString + '0';
80	}
81
82	rightNow_timeZoneString = rightNow_timeZoneString + rightNow_HoursDifference;
83
84	if (10 > rightNow_MinutesPart)
85	{
86		rightNow_timeZoneString = rightNow_timeZoneString + '0';
87	}
88
89	rightNow_timeZoneString = rightNow_timeZoneString + rightNow_MinutesPart;
90
91	if (printTheTimeZone)
92	{
93		document.writeln (rightNow_timeZoneString);
94	}
95
96	document.cookie = 'timezone=' + rightNow_timeZoneString + '; domain=' + theDomainForTheCookie;
97
98	return rightNow_timeZoneString;
99}	// End of tzCalculation_LocalTimeZone