seconds-to-date-string.js

const convert = seconds =>
  [
    { label: "year(s)", amount: 31104000 },
    { label: "month(s)", amount: 2592000 },
    { label: "week(s)", amount: 604800 },
    { label: "day(s)", amount: 86400 },
    { label: "hour(s)", amount: 3600 },
    { label: "minute(s)", amount: 60 },
    { label: "second(s)", amount: 1 }
  ]
    .reduce(
      ({ input, output }, { label, amount }) => {
        const total = Math.floor(input / amount);

        return {
          output: !total ? output : output.concat(`${total} ${label}`),
          input: input - total * amount
        };
      },
      { input: seconds, output: [] }
    )
    .output.join(", ");

console.clear();
console.log(convert(50));
console.log(convert(121));
console.log(convert(1000));
console.log(convert(3600));
console.log(convert(10000));
console.log(convert(604800));
console.log(convert(608400));
console.log(convert(100000));
console.log(convert(1000000));
console.log(convert(10000000));
console.log(convert(100000000));
console.log(convert(1000000000));