Date Validation - how to work around Javascript's auto-correcting of dates?

Question

I want to validate dates by Javascript and found this nice answer:

https://stackoverflow.com/a/1353711/3391783

but when i try to use it to validate dates, it seems like Javascript is auto-correcting my date by taking the closest valid date. so this will return true even though 2014-11-31 is not a valid date (Javascript months start at 0, so 10 equals November):

    function isValidDate(d) {
      if ( Object.prototype.toString.call(d) !== "[object Date]" )
        return false;
      return !isNaN(d.getTime());
    }
    
    var test_date = new Date(2014, 10, 31);
    
    console.log( test_date );
    console.log( isValidDate(test_date) );

seems like creating the Date is automatically switching it to 2014-12-01 which is a correct date. but I would like to be able to validate user input without changing it.

So how can i create an invalid new Date() in Javascript?
Or is there a much simpler way to do this?

score 3 · Accepted Answer · answered Nov 17 '14 at 11:16

3

You can use the auto-correction in the Date object to validate the date. Just check the input against what you have in the Date object:

var y = 2014, m = 10, d = 31;

var test_date = new Date(y, m, d);

var valid =
    test_date.getFullYear() == y &&
    test_date.getMonth() == m &&
    test_date.getDate() == d;

document.write(valid);

answered Nov 17 '14 at 11:16

Guffa

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oh, thanks. that's actually a cool solution. "if javascript decides to change my date - it has to be wrong" :) – low_rents Nov 17 '14 at 11:18

score 2 · Answer 2 · answered Nov 17 '14 at 11:09

2

When it comes to handling dates in JavaScript, I'm a big fan of Moment.js. As you can see here, they do a good job of validating dates: http://momentjs.com/docs/#/parsing/is-valid/

new Date(2013, 25, 14).toString(); // "Sat Feb 14 2015 00:00:00 GMT-0500 (EST)"
moment([2015, 25, 35]).format();   // 'Invalid date'

answered Nov 17 '14 at 11:09

Kristof Claes

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thanks. will try this library, but i kinda would like to restrict my work to `jQuery` and pure `Javascript`. – low_rents Nov 17 '14 at 11:19

score 0 · Answer 3 · answered Dec 19 '14 at 15:38

Here's a function I wrote a while back that demonstrates Guffa's solution.

    function isValidDate(checkDate) {
    if(!/\d\d\/\d\d\/\d\d\d\d/.test(checkDate)) {
            return false; // checkDate is not formatted as ##/##/####
        } else {
            // split checkDate into three pieces
            var strMM = checkDate.split('/')[0];
            var strDD = checkDate.split('/')[1];
            var strYYYY = checkDate.split('/')[2];

            // create new Date() object from split pieces
            var strDateCheck = new Date(strYYYY,(strMM - 1),strDD); 

            // evaluate each piece of resulting date object against each corresponding piece of checkDate
            if(((strDateCheck.getMonth() + 1) == strMM) && (strDateCheck.getDate() == strDD) && (strDateCheck.getFullYear() == strYYYY)) {
                /* if you wish, add additional validation constraints here */
                return true; // all three pieces match exactly
            } else {
                return false; // at least one piece did not match
            }
        }
    }

Date Validation - how to work around Javascript's auto-correcting of dates?

3 Answers3