Getting same unix time stamp for two different times in javascript

Question

I had two ical format timestamps and I want to convert them to normal time first and then to unix time.

Here this is the function I've been using to convert normal time to unix timestamp:

var normal_to_unix = function (date_string) {
    var date = new Date(date_string);
    return date.getTime() / 1000;
}

This function is fine since date is already in UTC and I need not do any conversions.

Now this is the function I've been using to convert ical time to unix time. The ical time in my case is like "20180603T150000Z".

var ics_to_unix = function (ics_string) {
    var year = ics_string.slice(0, 4);
    var month = ics_string.slice(4, 6);
    var date = ics_string.slice(6, 8);
    var hours = ics_string.slice(9, 11);
    var minutes = ics_string.slice(11, 13);
    var seconds = ics_string.slice(13, 15);
    var milliseconds = 0;
    console.log(year, month, date, hours, minutes, seconds, milliseconds); // This is example output 2018 06 03 15 00 00 0 
    return normal_to_unix((new Date(year, month, date, hours, minutes, seconds, milliseconds)).toDateString())
}

Now the problem is I'm getting the same unix time for "20180603T150000Z" and "20180603T160000Z" which are supposed to give different timestamps and it is 1530576000 for both of them.

Is there anything that I'm missing ? Thanks in advance.

Please have a look at this for live example

Answer 1

Several points here:

The toDateString() method returns the date portion of a Date object in human readable form in American English. For your example it is `Tue Jul 03 2018', perhaps that is not what you want.

new Date creates date in your local timezone, which could play well if you use it together with toString(), which will also return the string for date in your local timezone. But it will be subject to daylight saving changes, so I'd avoid using that method.

Another thing I'd like to avoid converting back and forth between strings and dates, since it does a lot of unnecessary computations.

I'd suggest to use the following:

var ics_to_unix = function (ics_string) {
  var year = parseInt(ics_string.slice(0, 4));
  var month = parseInt(ics_string.slice(4, 6)) - 1; // Jan is 0
  var date = parseInt(ics_string.slice(6, 8));
  var hours = parseInt(ics_string.slice(9, 11));
  var minutes = parseInt(ics_string.slice(11, 13));
  var seconds = parseInt(ics_string.slice(13, 15));

  return Date.UTC(year, month, date, hours, minutes, seconds) / 1000;
}

I have added explicit conversion of strings to numbers, adjusted the month to match what is used in javascript and also removed the extra call.