Compare date passed to new Date() with the date returned by new Date();

Question

I'm trying to check if a date is valid. If I pass 31/02/2018 to new Date it will return Tue Mar 03 1987 00:00:00 GMT+0000 (GMT) as 31/02/2018 is not a real date. So how can I compare the passed date with the return date of new Date? or am I going about this the wrong way altogether.

function isDateValid() {
    var dob = "31/02/1994",
        isValidDate = false;

    var reqs = dob.split("/"),
        day = reqs[0],
        month = reqs[1],
        year = reqs[2];

    var birthday = new Date(year + "-" + month + "-" + day);

    if (birthday === "????") {
        isValidDate = true;
    }

    return isValidDate;
}

Possible duplicate of [How to validate a date?](https://stackoverflow.com/questions/5812220/how-to-validate-a-date) — Fabio_MO, Jun 06 '18 at 14:37
Possible duplicate of [Detecting an "invalid date" Date instance in JavaScript](https://stackoverflow.com/questions/1353684/detecting-an-invalid-date-date-instance-in-javascript) — reisdev, Jun 06 '18 at 14:39

ssten · Answer 1 · 2018-06-06T15:04:19.160

2

You can get the last day of each month by doing this;

var lastDay = new Date(month, year, 0).getDate();

In your case;

function isDateValid(date){
    var isValidDate = false;

    var reqs = date.split("/"),
        day = reqs[0],
        month = reqs[1],
        year = reqs[2],
        lastDay = new Date(month, year, 0).getDate();

    if(day > 0 && day <= lastDay)
        isValidDate = true;

    return isValidDate;
}

edited Jun 06 '18 at 15:04

answered Jun 06 '18 at 14:40

ssten

1,848
1
16
28

This is not working correctly. `isDateValid("28/02/1994")` returns `false`. – mbuechmann Jun 06 '18 at 14:59
Sorry, it was checking if it was the last day of the month, now it checks if it's lower or equal to that day – ssten Jun 06 '18 at 15:05
`isDateValid("0/0/1")` returns true. Well, but that is just javascript... – mbuechmann Jun 06 '18 at 15:13
You are right. I guess I meant `isDateValid("1/0/0")`. – mbuechmann Jun 07 '18 at 06:00

Attersson · Accepted Answer · 2018-06-06T15:04:53.420

0

This is what you are looking for. I left your code unchanged and stuck to your original request.

function isDateValid() {
    var dob = "31/02/2018",
        isValidDate = false;

    var reqs = dob.split("/"),
        day = reqs[0],
        month = reqs[1],
        year = reqs[2];

    var birthday = new Date(year + "-" + month + "-" + day);
    
    if (+year  === birthday.getFullYear()&&
        +day   === birthday.getDate()    &&
        +month === birthday.getMonth() + 1) {
        isValidDate = true;
    }

    return isValidDate;
}

console.log(isDateValid());

edited Jun 06 '18 at 15:04

answered Jun 06 '18 at 14:50

Attersson

4,755
1
15
29

Welcome, glad to help. – Attersson Jun 06 '18 at 15:07

Compare date passed to new Date() with the date returned by new Date();

2 Answers2