Question

I want to do same thing as
How do I get the number of days between two dates in JavaScript?

but I want do the same on this date format: 2000-12-31.

Answer 1

function daysBetween(date1String, date2String){
  var d1 = new Date(date1String);
  var d2 = new Date(date2String);
  return (d2-d1)/(1000*3600*24);
}

console.log( daysBetween('2000-12-31', '2005-05-04') );  //-> 1585

ISO8601 date strings are recognized by JavaScript directly. No need to parse them yourself.