How do I do a Date comparison in Javascript?

Question

I would like to compare two dates in javascript. I have been doing some research, but all I can find is how to return the current date. I want to compare 2 separate dates, not related to today. How do I do that.

var startDate = Date(document.form1.Textbox2);

Answer 1

if (date1.getTime() > date2.getTime()) {
    alert("The first date is after the second date!");
}

Reference to Date object

Answer 2

new Date('1945/05/09').valueOf() < new Date('2011/05/09').valueOf()

Answer 3

JavaScript's dates can be compared using the same comparison operators the rest of the data types use: >, <, <=, >=, ==, !=, ===, !==.

If you have two dates A and B, then A < B if A is further back into the past than B.

But it sounds like what you're having trouble with is turning a string into a date. You do that by simply passing the string as an argument for a new Date:

var someDate = new Date("12/03/2008");

or, if the string you want is the value of a form field, as it seems it might be:

var someDate = new Date(document.form1.Textbox2.value);

Should that string not be something that JavaScript recognizes as a date, you will still get a Date object, but it will be "invalid". Any comparison with another date will return false. When converted to a string it will become "Invalid Date". Its getTime() function will return NaN, and calling isNaN() on the date itself will return true; that's the easy way to check if a string is a valid date.

Answer 4

You can use the getTime() method on a Date object to get the timestamp (in milliseconds) relative to January 1, 1970. If you convert your two dates into integer timestamps, you can then compare the difference by subtracting them. The result will be in milliseconds so you just divide by 1000 for seconds, then 60 for minutes, etc.

Answer 5

I would rather use the Date valueOf method instead of === or !==

Seems like === is comparing internal Object's references and nothing concerning date.

Answer 6

function fn_DateCompare(DateA, DateB) {     // this function is good for dates > 01/01/1970

    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;  // lt
    else if (parseFloat(msDateA) == parseFloat(msDateB))
      return 0;  // eq
    else if (parseFloat(msDateA) > parseFloat(msDateB))
      return 1;  // gt
    else
      return null;  // error
}

Answer 7

    function validateform()
    {
     if (trimAll(document.getElementById("<%=txtFromDate.ClientID %>").value) != "") {
   if (!isDate(trimAll(document.getElementById("<%=txtFromDate.ClientID %>").value)))
         msg = msg + "<li>Please enter valid From Date in mm/dd/yyyy format\n";
   else {
       var toDate = new Date();
       var txtdate = document.getElementById("<%=txtFromDate.ClientID %>").value;
       var d1 = new Date(txtdate)
   if (Date.parse(txtdate) > Date.parse(toDate)) {                   
         msg = msg + "<li>From date must be less than or equal to today's date\n";
   }
  }
}

     if (trimAll(document.getElementById("<%=txtToDate.ClientID %>").value) != "") {
            if (!isDate(trimAll(document.getElementById("<%=txtToDate.ClientID %>").value)))
                msg = msg + "<li>Please enter valid To Date in mm/dd/yyyy format\n";
            else {
                var toDate = new Date();
                var txtdate = document.getElementById("<%=txtToDate.ClientID %>").value;
                var d1 = new Date(txtdate)

                if (Date.parse(txtdate) > Date.parse(toDate)) {
                    msg = msg + "<li>To date must be less than or equal to today's date\n"; 
                  }
                 }
                }

Answer 8

You could try adding the following script code to implement this:

if(CompareDates(smallDate,largeDate,'-') == 0) {
    alert('Selected date must be current date or previous date!');
return false;
}

function CompareDates(smallDate,largeDate,separator) {
    var smallDateArr = Array();
    var largeDateArr = Array(); 
    smallDateArr = smallDate.split(separator);
    largeDateArr = largeDate.split(separator);  
    var smallDt = smallDateArr[0];
    var smallMt = smallDateArr[1];
    var smallYr = smallDateArr[2];  
    var largeDt = largeDateArr[0];
    var largeMt = largeDateArr[1];
    var largeYr = largeDateArr[2];

    if(smallYr>largeYr) 
        return 0;
else if(smallYr<=largeYr && smallMt>largeMt)
    return 0;
else if(smallYr<=largeYr && smallMt==largeMt && smallDt>largeDt)
    return 0;
else 
    return 1;
}  

Answer 9

You can try this code for checking which date value is the highest from two dates with a format MM/DD/YYYY:

function d_check() {
    var dl_sdt=document.getElementIdBy("date_input_Id1").value; //date one
    var dl_endt=document.getElementIdBy("date_input_Id2").value; //date two

    if((dl_sdt.substr(6,4)) > (dl_endt.substr(6,4))) {
        alert("first date is greater");
        return false;
    }

    else if((((dl_sdt.substr(0,2)) > (dl_endt.
        substr(0,2)))&&(frdt(dl_sdt.substr(3,2)) > (dl_endt.substr(3,2))))||
        (((dl_sdt.substr(0,2)) > (dl_endt.substr(0,2)))&&
        ((dl_sdt.substr(3,2)) < (dl_endt.substr(3,2))))||
        (((dl_sdt.substr(0,2)) == (dl_endt.substr(0,2)))&&((dl_sdt.substr(3,2)) > 
        (dl_endt.substr(3,2))))) {
            alert("first date is greater");
        return false;
    }

    alert("second date is digher");
    return true;
}

/*for checking this....create a form and give id's to two date inputs.The date format should be mm/dd/yyyy or mm-dd-yyyy or mm:dd:yyyy or mm.dd.yyyy like this. */