Question

Determining a user’s timezone server side and converting from UTC has proven more trouble than its worth.

Is there a reliable way for javascript/jquery to determine the timezone of the user and apply the offset to a UTC datetime stamp (2012-08-25 10:59:56.511479) and output in my desired format (Aug 25 ’12 – 10:59AM)?

What might the jquery code look like to say

// dom ready
$('span.localtime').each(function(e) {
    // get stamp and apply conversion
});

Answer 1

.getTimezoneOffset() is available on the date object, and gives you the offset from UTC in minutes.

var offset = (new Date()).getTimezoneOffset();

// convert myUtcDate to a date in local time
myUtcDate.setMinutes(myUtcDate.getMinutes() + (offset*-1));

Thus:

$('.span.localtime').each(function() {
   var myUtcDate = new Date($(this).html()); // assuming "2012-08-25 10:59:56.511479"
   myUtcDate.setMinutes(myUtcDate.getMinutes() + (myUtcDate.getTimezoneOffset() * -1));

   $(this).html(myUtcDate.toString());
});

Note that myUtcDate.toString() could be replaced with any date formatting you want. In your case, it might look like

$(this).html(formatDate(myUtcDate));

function formatDate(d) {

   var months = ['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'];

    var y = d.getFullYear().toString().slice(-2); // "12"
    var m = months[d.getMonth()]; // "Aug"
    var d = d.getDate(); // "25"

    var ampm = 'AM';
    var h = d.getHours();

    if(h>=12) {
        h -= 12;
        ampm = 'PM';
    }

    if(h == 0)
       h = 12;

    var min = ("00" + d.getMinutes()).slice(-2);

    return m + " " + d + " '" + y + " - " + h + ":" + min + ampm;
}

You might want to use a date format plugin for formatting dates in a neater more reliable manner.