Detecting an “invalid date” Date instance in JavaS

Question

I'd like to tell the difference between valid and invalid date objects in JS, but couldn't figure out how:

var d = new Date("foo");
console.log(d.toString()); // shows 'Invalid Date'
console.log(typeof d); // shows 'object'
console.log(d instanceof Date); // shows 'true'

Any ideas for writing an isValidDate function?

• Ash recommended Date.parse for parsing date strings, which gives an authoritative way to check if the date string is valid.
• What I would prefer, if possible, is have my API accept a Date instance and to be able to check/assert whether it's valid or not. Borgar's solution does that, but I need to test it across browsers. I also wonder whether there's a more elegant way.
• Ash made me consider not having my API accept Date instances at all, this would be easiest to validate.
• Borgar suggested testing for a Date instance, and then testing for the Date's time value. If the date is invalid, the time value is NaN. I checked with ECMA-262 and this behavior is in the standard, which is exactly what I'm looking for.

Answer 1

A ready function based on top rated answer:

  /**
   * Check if date exists and is valid.
   *
   * @param {String} dateString Date in YYYY-mm-dd format.
   */
  function isValidDate(dateString) {
  var isValid = false;
  var date;

  date =
    new Date(
      dateString);

  if (
    Object.prototype.toString.call(
      date) === "[object Date]") {

    if (isNaN(date.getTime())) {

      // Date is unreal.

    } else {
      // Date is real if month and day match each other in date and string (otherwise may be shifted):
      isValid =
        date.getUTCMonth() + 1 === dateString.split("-")[1] * 1 &&
        date.getUTCDate() === dateString.split("-")[2] * 1;
    }
  } else {
    // It's not a date.
  }

  return isValid;
}

Answer 2

I use the following code to validate values for year, month and date.

function createDate(year, month, _date) {
  var d = new Date(year, month, _date);
  if (d.getFullYear() != year 
    || d.getMonth() != month
    || d.getDate() != _date) {
    throw "invalid date";
  }
  return d;
}

For details, refer to Check date in javascript

Answer 3

I've written this function. Pass it a string parameter and it will determine whether it's a valid date or not based on this format "dd/MM/yyyy".

here is a test

input: "hahaha",output: false.

input: "29/2/2000",output: true.

input: "29/2/2001",output: false.

function isValidDate(str) {
    var parts = str.split('/');
    if (parts.length < 3)
        return false;
    else {
        var day = parseInt(parts[0]);
        var month = parseInt(parts[1]);
        var year = parseInt(parts[2]);
        if (isNaN(day) || isNaN(month) || isNaN(year)) {
            return false;
        }
        if (day < 1 || year < 1)
            return false;
        if(month>12||month<1)
            return false;
        if ((month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) && day > 31)
            return false;
        if ((month == 4 || month == 6 || month == 9 || month == 11 ) && day > 30)
            return false;
        if (month == 2) {
            if (((year % 4) == 0 && (year % 100) != 0) || ((year % 400) == 0 && (year % 100) == 0)) {
                if (day > 29)
                    return false;
            } else {
                if (day > 28)
                    return false;
            }      
        }
        return true;
    }
}

Answer 4

None of these answers worked for me (tested in Safari 6.0) when trying to validate a date such as 2/31/2012, however, they work fine when trying any date greater than 31.

So I had to brute force a little. Assuming the date is in the format mm/dd/yyyy. I am using @broox answer:

Date.prototype.valid = function() {
    return isFinite(this);
}    

function validStringDate(value){
    var d = new Date(value);
    return d.valid() && value.split('/')[0] == (d.getMonth()+1);
}

validStringDate("2/29/2012"); // true (leap year)
validStringDate("2/29/2013"); // false
validStringDate("2/30/2012"); // false

Answer 5

Would like to mention that the jQuery UI DatePicker widget has a very good date validator utility method that checks for format and validity (e.g., no 01/33/2013 dates allowed).

Even if you don't want to use the datepicker widget on your page as a UI element, you can always add its .js library to your page and then call the validator method, passing the value you want to validate into it. To make life even easier, it takes a string as input, not a JavaScript Date object.

See: http://api.jqueryui.com/datepicker/

It's not listed as a method, but it is there-- as a utility function. Search the page for "parsedate" and you'll find:

$.datepicker.parseDate( format, value, settings ) - Extract a date from a string value with a specified format.

Example usage:

var stringval = '01/03/2012';
var testdate;

try {
  testdate = $.datepicker.parseDate('mm/dd/yy', stringval);
             // Notice 'yy' indicates a 4-digit year value
} catch (e)
{
 alert(stringval + ' is not valid.  Format must be MM/DD/YYYY ' +
       'and the date value must be valid for the calendar.';
}

(More info re specifying date formats is found at http://api.jqueryui.com/datepicker/#utility-parseDate)

In the above example, you wouldn't see the alert message since '01/03/2012' is a calendar-valid date in the specified format. However if you made 'stringval' equal to '13/04/2013', for example, you would get the alert message, since the value '13/04/2013' is not calendar-valid.

If a passed-in string value is successfully parsed, the value of 'testdate' would be a Javascript Date object representing the passed-in string value. If not, it'd be undefined.

Answer 6

you can check the valid format of txDate.value with this scirpt. if it was in incorrect format the Date obejct not instanced and return null to dt .

 var dt = new Date(txtDate.value)
 if (isNaN(dt))

And as @MiF's suggested in short way

 if(isNaN(new Date(...)))