I am trying to compare two dates. I have this code which I thought would work a treat, but it didn't. For now I just want to alert with an error if the end date is less than the start date. The date style, yyyy-mm-dd, needs to be kept in this format for other events prior to this. What is wrong with this code?

   startdate = "2009-11-01" ;
   enddate  = "2009-11-04" ;

   var d1 = new Date(startdate)
   var d2 = new Date(enddate)

   if (d2 < d1) {
      alert ("Error ! ) ;
   }

   document.cookie='st =' + startdate // set sytem cookie
   document.cookie='en =' + enddate
   window.location = self.location.href
   window.opener.location.reload()
   close()

I am trying to compare two dates. I have this code which I thought would work a treat, but it didn't. For now I just want to alert with an error if the end date is less than the start date. The date style, yyyy-mm-dd, needs to be kept in this format for other events prior to this. What is wrong with this code?

   startdate = "2009-11-01" ;
   enddate  = "2009-11-04" ;

   var d1 = new Date(startdate)
   var d2 = new Date(enddate)

   if (d2 < d1) {
      alert ("Error ! ) ;
   }

   document.cookie='st =' + startdate // set sytem cookie
   document.cookie='en =' + enddate
   window.location = self.location.href
   window.opener.location.reload()
   close()

• javascript

• You can compare 'yyyy-mm-dd' date strings lexicographically: enddate < startdate – Robert Commented Dec 19, 2014 at 13:27

7 Answers 7

Try using DateJS, an open-source JavaScript Date Library that can handle pretty much everything! The following example is working:

<script type="text/javascript" src="date.js"></script>
<script>

    startdate = "2009-11-01";
    enddate  = "2009-11-04"; 

    var d1 = Date.parse(startdate);
    var d2 = Date.parse(enddate) ;

    if (d1 < d2) {
        alert ("Error!");
    }

</script>

Someone finally uses ISO 8601 standard dates but then ...

You are using a nice international standard that JavaScript arguably should understand. But it doesn't.

The problem is that your dates are in ISO 8601 standard format which the built-in Date.parse() can't read.

JavaScript implements the older IETF dates from RFC 822/1123. One solution is to tweak them into the RFC-style, which you can see in RFC1123, and which look like dd month yyyy.

There is coding floating about that can scan the ISO format comprehensively, and now that you know to google for "iso standard date" you can get it. Over here I found this:

Date.prototype.setISO8601 = function (string) {
    var regexp = "([0-9]{4})(-([0-9]{2})(-([0-9]{2})" +
        "(T([0-9]{2}):([0-9]{2})(:([0-9]{2})(\.([0-9]+))?)?" +
        "(Z|(([-+])([0-9]{2}):([0-9]{2})))?)?)?)?";
    var d = string.match(new RegExp(regexp));

    var offset = 0;
    var date = new Date(d[1], 0, 1);

    if (d[3]) { date.setMonth(d[3] - 1); }
    if (d[5]) { date.setDate(d[5]); }
    if (d[7]) { date.setHours(d[7]); }
    if (d[8]) { date.setMinutes(d[8]); }
    if (d[10]) { date.setSeconds(d[10]); }
    if (d[12]) { date.setMilliseconds(Number("0." + d[12]) * 1000); }
    if (d[14]) {
        offset = (Number(d[16]) * 60) + Number(d[17]);
        offset *= ((d[15] == '-') ? 1 : -1);
    }

    offset -= date.getTimezoneOffset();
    time = (Number(date) + (offset * 60 * 1000));
    this.setTime(Number(time));
}

js> t = new Date()
Sun Nov 01 2009 09:48:41 GMT-0800 (PST)
js> t.setISO8601("2009-11-01")
js> t

Sat Oct 31 2009 17:00:00 GMT-0700 (PDT)

The 11-01 is reinterpreted in my timezone, as long as all your dates get the same conversion then they should compare reasonably, otherwise you can add TZ info to your string or to the Date object.

The Date constructor cannot parse that format, and since you cannot change it, you should parse it manually, and pass the year, month and date parts to it, for example:

function compareDates(startDate, endDate) {

  // parse a date in yyyy-mm-dd format
  function parseDate(input) {
    var parts = input.match(/(\d+)/g);
    return new Date(parts[0], parts[1]-1, parts[2]); // months are 0-based
  }

  if (parseDate(endDate) < parseDate(startDate)) {
    alert ("Error !");
  }
}

Usage:

var startDate = "2009-11-01",
    endDate = "2009-11-04";
compareDates(startDate, endDate);    

var myDate=new Date();
myDate.setFullYear(2010,0,14);
var today = new Date();

if (myDate>today)
{
    alert("Today is before 14th January 2010");
}
else
{
    alert("Today is after 14th January 2010");
}

source: http://www.w3schools.com/jS/js_obj_date.asp

If you only need to know if one date comes before the other, you could just use the Date object's getTime() method to compare their respective numbers of milliseconds since midnight Jan 1, 1970:

if( d2.getTime() < d1.getTime() )
{
    alert("eeeek!");
}

--- Don't get mixed up and try to use getMilliseconds(), though :)

w3schools documentation on getTime()

USe this function for date comparison in javascript:

    function fn_DateCompare(DateA, DateB) {
      var a = new Date(DateA);
      var b = new Date(DateB);

      var msDateA = Date.UTC(a.getFullYear(), a.getMonth()+1, a.getDate());
      var msDateB = Date.UTC(b.getFullYear(), b.getMonth()+1, b.getDate());

      if (parseFloat(msDateA) < parseFloat(msDateB))
        return -1;  // less than
      else if (parseFloat(msDateA) == parseFloat(msDateB))
        return 0;  // equal
      else if (parseFloat(msDateA) > parseFloat(msDateB))
        return 1;  // greater than
      else
        return null;  // error
  }

I implemented the below code for a date comparison depending on current time - -

// get the current time from a hidden input which is being set by server time 
// because client may have a wrong time
var ch = jQuery('#clockHours').val(); // e.g. 9,10 etc.
ch = parseInt(ch);
// get the today's date from a server value as well
var td = jQuery('#clockDate').val(); // may be => new Date(); e.g. 2014-05-15
td = Date.parse(td);
td.setHours(0, 0, 0, 0);
// get the input date
var inpdate = jQuery('#jform_in_date').val(); // may be => new Date(); e.g. 2014-05-15
inpdate = Date.parse(inpdate);
inpdate.setHours(0, 0, 0, 0);
// get yesterday's date. this is from server as well
yd = new Date();
yd.setFullYear(td.getFullYear(), td.getMonth(), td.getDate()-1);
yd.setHours(0, 0, 0, 0);
alert('today\'s date is: '+td.toString());
alert('yesterday\'s date is: '+yd.toString());
// if it is not 10 AM then dates from yesterday are valid
if(ch <= 9) {
   if(inpdate.getTime() >= yd.getTime()) {
       alert('Valid: dates from yesterday are allowed');
   } else {
       alert('Invalid: dates before yesterday are not allowed');
   }
} else {
   if(inpdate.getTime() >= td.getTime()) {
       alert('Valid: dates from today are allowed');
   } else {
       alert('Invalid: dates before today are not allowed');
   }
}

I hope this will help very clearly.