```
//Introduction
// 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:
// formatDuration(62) // returns "1 minute and 2 seconds"
// formatDuration(3662) // returns "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.
//The best practice
function formatDuration (seconds) {
var time = { year: 31536000, day: 86400, hour: 3600, minute: 60, second: 1 },
res = [];
if (seconds === 0) return 'now';
for (var key in time) {
if (seconds >= time[key]) {
var val = Math.floor(seconds/time[key]);
res.push(val += val > 1 ? ' ' + key + 's' : ' ' + key);
seconds = seconds % time[key];
}
}
return res.length > 1 ? res.join(', ').replace(/,([^,]*)$/,' and'+'$1') : res[0]
}
```