human-readable-duration-format.js

// Your task in order to complete this Kata is to write a function which formats a duration, given as a number of seconds, in a human-friendly way.

// The function must accept a non-negative integer. If it is zero, it just returns "now". Otherwise, the duration is expressed as a combination of years, days, hours, minutes and seconds.

// It is much easier to understand with an example:

// * For seconds = 62, your function should return 
//     "1 minute and 2 seconds"
// * For seconds = 3662, your function should return
//     "1 hour, 1 minute and 2 seconds"
// For the purpose of this Kata, a year is 365 days and a day is 24 hours.

// Note that spaces are important.

// Detailed rules
// The resulting expression is made of components like 4 seconds, 1 year, etc. In general, a positive integer and one of the valid units of time, separated by a space. The unit of time is used in plural if the integer is greater than 1.

// The components are separated by a comma and a space (", "). Except the last component, which is separated by " and ", just like it would be written in English.

// A more significant units of time will occur before than a least significant one. Therefore, 1 second and 1 year is not correct, but 1 year and 1 second is.

// Different components have different unit of times. So there is not repeated units like in 5 seconds and 1 second.

// A component will not appear at all if its value happens to be zero. Hence, 1 minute and 0 seconds is not valid, but it should be just 1 minute.

// A unit of time must be used "as much as possible". It means that the function should not return 61 seconds, but 1 minute and 1 second instead. Formally, the duration specified by of a component must not be greater than any valid more significant unit of time.

function formatDuration (seconds) {
  const ref = { year: 31536000, day: 86400, hour: 3600, minute: 60, second: 1 }
  res = [];
  
  if (seconds === 0) return 'now';
  
  for (var key in ref) {
    if (seconds >= ref[key]) {
      var val = Math.floor(seconds/ref[key]);
      res.push(val += val > 1 ? ' ' + key + 's' : ' ' + key);
      seconds = seconds % ref[key];
    }
  }
  return res.length > 1 ? res.join(', ').replace(/,([^,]*)$/,' and'+'$1') : res[0]
}