javascript validation for dates takes string for comparison

Sometime back i had asked question in SO as to how to validate startdate < enddate.

The JS that i had written is as below;

function DateValidation(startDate, endDate) {
                if (startDate != ' ' && endDate != ' ') 
                {
                    var stdate = Date.parse(startDate);
                    var enddate = Date.parse(endDate);
                    if (stdate > enddate) 
                    {
                        alert('Start date cannot be greater than end date!');
                        return false;
                    }
                    else 
                {
                    return true;
                }
               }
            }

The function gets called on the click of the sub开发者_如何学Pythonmit button. It is register as;

OnClientClick="javascript: return DateValidation(window.document.getElementById('txtStartDate').value,window.document.getElementById('txtEndDate').value);"

Now assume that start date is October 4 2011 (04/10/2011) and end date is December 2 2011 (02/12/2011). In this case the alert should NOT get fired but it still gets fired up (because 04 > 02).

What mistake am i making here?

---

Your startDate & endDate parameters should be in mm/dd/yyyy format. But you provided them as dd/mm/yyyy format, so the unexpected thing occured.

I've faced this kinda probs B4. If your website's clients are all about to type in date time in format "dd/mm/yyyy", so you need a "correctDate()" function to replace date part with month part in the input-date-string.

The function may look like this :

function correctDate(D){
       var D=D.split('/');
       return D[1]+'/'+D[0]+'/'+D[2]
}
//input :  2/10/2011 , output :  10/2/2011

And in the DateValidation() function, you can use it like this:

....
      var stdate = Date.parse( correctDate(startDate) );
      var enddate = Date.parse( correctDate(endDate) );
      if (stdate > enddate){
....

---

<script type="text/javascript">
var d = Date.parse("Jul 8, 2005");
document.write(d);
</script>

The output of the code above will be: 1120773600000

So your reasoning cannot be right. Try to alert the stdate and enddate after parsing. Something is happening there.

---

The mistake that you are making is that Date.parse interprets xx/xx/xxxx formatted strings as U.S. style dates with the month first. 04/10/2011 is taken as April 10, not October 4.

Here is a transcript:

> var startDate = '04/10/2011';var stdate = Date.parse(startDate)
> startDate
04/10/2011
> stdate
1302418800000
> var endDate = '02/12/2011';var enddate = Date.parse(endDate);
> endDate
02/12/2011
> enddate
1297497600000
> stdate > enddate
true

IMHO you should avoid ambiguous date formats like this. If date strings are to be used, force users to enter ISO8601 (yyyy/MM/dd) formatted text.

There is decent support for ISO8601 in ECMAScript 5 browsers. Also see the Date.js library. Or also this SO question for more info.

ADDENDUM

The built-in Date.parse function is documented here. You can see it does not support DD/MM/YYYY. While an evil programmer could accept a string in the form DD/MM/YYYY and use substring and concat (or regexes) to rewrite in an acceptable format for Date.parse, I'll assume you are not an evil programmer.

The proper solution is to use a date parser that accepts format strings. For JavaScript, one such library is Date.js. It will allow you to write the following:

Date.parseExact("20/04/2011", "dd/MM/yyyy");

and get the date object corresponding to April 20, 2011.