const dateMinus = require('./').dateMinus;
var preDate = (new Date()).setFullYear(2009);
var howlong = dateMinus(preDate);

{
  "years": 8,
  "months": 0,
  "days": 0,
  "hours": "00",
  "minutes": "00",
  "seconds": "00",
  "passed": true, // date相对current为过去时间(date is earlier than current.)
  "date": "2009-09-22T15:52:28.861Z",
  "current": "2017-09-22T15:52:28.862Z"
}