Question

I trying to create a very simple time difference calculation. Just “endtime – starttime”. I’m getting +1 hour though. I suspect it has with my timezone to do, since I’m GMT+1.

Regardless, that should not affect the difference, since both start and end times are in the same timezone.

Check my running example-code here:

http://jsfiddle.net/kaze72/Rm3f3/

$(document).ready(function() {
    var tid1 =  (new Date).getTime();

    $("#tid").click(function() {
        var nu = (new Date).getTime();
        var diff = new Date(nu - tid1);
        console.log(diff.getUTCHours() + ":" +
                diff.getUTCMinutes() + ":" +
               diff.getUTCSeconds());  
        console.log(diff.toLocaleTimeString());
    });
})

Answer 1

You must understand what Date object represent and how it stores dates. Basically each Date is a thin wrapper around the number of milliseconds since 1970 (so called epoch time). By subtracting one date from another you don’t get a date: you just get the number of milliseconds between the two.

That being said this line doesn’t have much sense:

var diff = new Date(nu - tid1);

What you really need is:

var diffMillis = nu - tid1;

…and then simply extract seconds, minutes, etc.:

var seconds = Math.floor(diffMillis / 1000);
var secondsPart = seconds % 60;
var minutes = Math.floor(seconds / 60);
var minutesPart = minutes % 60;
var hoursPart = Math.floor(minutes / 60);
//...
console.log(hoursPart + ":" + minutesPart + ":" + secondsPart);  

Working fiddle.