Question

On a website (http://webdesign.onyou.ch/2010/08/04/javascript-time-ago-pretty-date/) I found this very useful function, you give it an ISO 8601 time (for example 2010-08-26T22:24:17Z) and it outputs the time that has passed since this timestamp. But because of I want to use UTC ISO 8601 timestamps, so my app can be used internationally, for example, if you’re in Europe, it alway says “3 hours ago”, even if the message has been posted a few seconds ago.

So how can I make it return how much time has passed since the input UTC timestamp and the current UTC time?

    function relativeTime(date_str){
    var time_formats = [
    [60, 'seconds', 1], // 60
    [120, '1 minute ago', '1 minute from now'], // 60*2
    [3600, 'minutes', 60], // 60*60, 60
    [7200, '1 hour ago', '1 hour from now'], // 60*60*2
    [86400, 'hours', 3600], // 60*60*24, 60*60
    [172800, 'yesterday', 'tomorrow'], // 60*60*24*2
    [604800, 'days', 86400], // 60*60*24*7, 60*60*24
    [1209600, 'last week', 'next week'], // 60*60*24*7*4*2
    [2419200, 'weeks', 604800], // 60*60*24*7*4, 60*60*24*7
    [4838400, 'last month', 'next month'], // 60*60*24*7*4*2
    [29030400, 'months', 2419200], // 60*60*24*7*4*12, 60*60*24*7*4
    [58060800, 'last year', 'next year'], // 60*60*24*7*4*12*2
    [2903040000, 'years', 29030400], // 60*60*24*7*4*12*100, 60*60*24*7*4*12
    [5806080000, 'last century', 'next century'], // 60*60*24*7*4*12*100*2
    [58060800000, 'centuries', 2903040000] // 60*60*24*7*4*12*100*20, 60*60*24*7*4*12*100
    ];
    var time = ('' + date_str).replace(/-/g,"/").replace(/[TZ]/g," ").replace(/^\s\s*/, '').replace(/\s\s*$/, '');
    if(time.substr(time.length-4,1)==".") time =time.substr(0,time.length-4);
    var seconds = (new Date - new Date(time)) / 1000;
    var token = 'ago', list_choice = 1;
    if (seconds < 0) {
        seconds = Math.abs(seconds);
        token = 'from now';
        list_choice = 2;
    }
    var i = 0, format;
    while (format = time_formats[i++])
        if (seconds < format[0]) {
            if (typeof format[2] == 'string')
                return format[list_choice];
            else
                return Math.floor(seconds / format[2]) + ' ' + format[1] + ' ' + token;
        }
    return time;
}

Answer 1

Change

var seconds = (new Date - new Date(time)) / 1000;

to

var seconds = (new Date - new Date(time)) / 1000 + (new Date).getTimezoneOffset()*60;

I didn’t tested your code before posting, so here’s the document for getTimezoneOffset:
https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Date/getTimezoneOffset