My translation from Ruby to JavaScript gives different results

I am writing a function that takes a future date and returns a string in the form "X weeks, Y days, Z hours"

representing a countdown to that date. My approach:

• Get the number of seconds separating two dates by subtracting the epoch time of the future date from today.
• Divide the number of seconds by 604800 (number of seconds per week). Save the result as weeks
  
  and override seconds
  
  as remainder (which is what Ruby does divmod
  
  ).
• Do the same for days
  
  , hours
  
  and minutes
  
  .

I first wrote it in Ruby, which works:

def time_countdown(*date_string)
  seconds = Time.new(*date_string).to_i - Time.now.to_i

  weeks, seconds = seconds.divmod 604800
  days, seconds = seconds.divmod 86400
  hours, seconds = seconds.divmod 3600
  minutes, seconds = seconds.divmod 60

  return "#{weeks} weeks, #{days} days, #{hours} hours."   
end

      

        
        
        
      

    

I translated this to JavaScript with the same approach, except for the following:

• Since JavaScript is missing divmod
  
  , I did it manually, first setting weeks
  
  / days
  
  / hours
  
  and then setting seconds
  
  to the remainder.
• I need to use Math.floor
  
  because JavaScript exclusively uses floats.
• I am dividing the epoch time by 1000 because JS uses milliseconds for its timestamps, unlike Ruby.
• The My JS function expects to receive an integer epochTime since I haven't learned how to pass arbitrary arguments in JS.

Code:

function timeCountdown(epochTime) {
    var seconds = epochTime/1000 - new Date().getTime() / 1000;

    var weeks = Math.floor(seconds / 604800);
    seconds = seconds % 604800;
    var days = Math.floor(seconds / 86400);
    seconds = seconds % 86400;
    var hours = Math.floor(seconds / 3600);
    seconds = seconds % 3600;

    return weeks + " weeks, " + days + " days, " + hours + " hours.";
}

      

        
        
        
      

    

As 2015,6,19

of June 1st, JS gives "6 weeks, 5 days, 21 hours"

and Ruby gives "2 weeks, 3 days, 6 hours"

. I cannot figure out where this difference is. Can anyone point out my mistake?