Local time display from the date of an era

Question

I am trying to show when a record was saved in local time using javascript date. The problem is that the date of the era is stuck in the CDT.

Suppose I saved a record at 9:18 a.m. CDT, this is included in the database as the js date value of the era 1349896693626. My code is as follows:

var savedTime = 1349896693626; var sDate = new Date(); sDate.setTime(Number(savedTime)); var offset = sDate.getTimezoneOffset(); //grabbing offset and changing it to milliseconds to adjust time var milliOffset = offset * 60 * 1000; var adjustedDate = Number(savedTime) - milliOffset; var displayDate = new Date(adjustedDate); alert("date is " + displayDate); 

I expect the displayDate to show 9:18 in the morning, and this will happen if I'm in the CDT, but if I go to PDT, it will display 5:18 in the morning, and I don’t understand why. This is similar to the fact that I need to hard-adjust the 5-hour offset (CDT offset) to make it work, but that doesn't make any sense. Can anyone explain what is happening?

thanks

Answer 1

To display a specific time zone line, ignore the local time zone.

You will only be interested in GMT and the correct offset for the target time zone.

Central time is 6 or 5 hours behind GMT, depending on the range that DST applies.

 // standard time offsets Date.tzones={ N:['Newfoundland', -210], A:['Atlantic', -240], E:['Eastern', -300], C:['Central', -360], M:['Mountain', -420], P:['Pacific', -480], AK:['Alaska', -540], HA_:['Hawaii-Aleutian (Aleutian)', -600], HA:['Hawaii-Aleutian (Hawaii)', -600, -1] }; //find the offset, accurate for US time zones since 2006 Date.dstOff= function(d, tz){ var off= tz[1], countstart, countend, dstart, dend; var y= d.getUTCFullYear(); if(off && tz[2]!= -1){ countstart= 8, countend= 1, dstart= new Date(Date.UTC(y, 2, 8, 2)), dend= new Date(Date.UTC(y, 10, 1, 2)); while(dstart.getUTCDay()!== 0) dstart.setUTCDate(++countstart); while(dend.getUTCDay()!== 0) dend.setUTCDate(++countend); dstart.setUTCMinutes(off); dend.setUTCMinutes(off); if(dstart<= d && dend>= d) off+= 60; } return off; } //format the result: Date.short_months= ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']; Date.toTZString= function(d, tzp){ d= d? new Date(d):new Date(); tzp= tzp || 'G'; var h, m, apm= 'pm', off, dst, label= tzp+'ST', str, tz= Date.tzones[tzp.toUpperCase()]; if(!tz) tz= ['Greenwich', 0]; off= tz[1]; if(off){ dst= Date.dstOff(d, tz); if(dst!== off) label= tzp+'DT'; d.setUTCMinutes(d.getUTCMinutes()+dst); } else label= 'GMT'; h= d.getUTCHours(); m= d.getUTCMinutes(); if(h>12) h-= 12; else if(h!== 12) apm= 'am'; if(h== 0) h= 12; if(m<10) m= '0'+m; var str= Date.short_months[d.getUTCMonth()]+' '+d.getUTCDate()+', '; return str+ h+':'+m+' '+apm+' '+label.toUpperCase(); }; 

var d = new Date (1349896693626);

alert ('Central time:' + Date.toTZString (d, 'C'));

return value: (String) Central time: October 10, 14:18 CDT