Date Validation using regex

Question

Below code is an existing code in my working project and I didn't start it. All I know is that this code is validating a Date if it is valid or invalid format.

function isValidDate(div, field) {
    var reg = /^((0?\d)|(1[012]))\/([012]?\d|30|31)\/\d{1,4}$/;
    var dateField = $("#" + div + " #" + field + "").val();
    if ((dateField == "") || (dateField == "1/1/0001") || (dateField == "MM/dd/yyyy"))
    {
        alert('Invalid Date.');
        return false;
    } else {
        if (reg.test(dateField) == false) {
            alert('Invalid Date.');
            return false;
        } else {
            return true;
        }
    }
}

My question is please tell me what is what does really the purpose of this line var reg = /^((0?\d)|(1[012]))\/([012]?\d|30|31)\/\d{1,4}$/; What this code really do and if possible can explain it step by step because I am really noob in regex I can't even read it. Thanks.

Have a look at regex 101, enter the regex there and it get explained: https://regex101.com/r/2tN1Rt/1 — Igl3, Oct 10 '16 at 08:21
Or [with an example string](https://regex101.com/r/2l38iS/1). — Wiktor Stribiżew, Oct 10 '16 at 08:21
@WiktorStribiżew how can i change the format from `/` into `-`? — Trafalgar D Law, Oct 10 '16 at 08:32
To support both - `/^((0?\d)|(1[012]))[\/-]([012]?\d|30|31)[\/-]\d{1,4}$/` or `/^(?:0?\d|1[012])([\/-])(?:[012]?\d|30|31)\1\d{1,4}$/` — Wiktor Stribiżew, Oct 10 '16 at 09:08
@WiktorStribiżew lastly. How to make `MM/dd/yyyy` read it as valid?. — Trafalgar D Law, Oct 10 '16 at 09:18
Sorry, no idea what you mean.I guess you can just parse the input as a `Date` object and see if the data received is correct. You can grab day, month, year info with capturing groups - `/^((0?\d)|(1[012]))[\/-]([012]?\d|30|31)[\/-]\d{1,4}$/ or /^(0?\d|1[012])([\/-])([012]?\d|30|31)\2(\d{1,4})$/` (days - Group 1, months - Group 3 and years - Group 4). — Wiktor Stribiżew, Oct 10 '16 at 09:21
I have a default value of `MM/dd/yyyy` and I use the code but it can't read the `MM/dd/yyyy` — Trafalgar D Law, Oct 10 '16 at 09:24
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/125314/discussion-between-trafalgar-d-law-and-wiktor-stribizew). — Trafalgar D Law, Oct 10 '16 at 09:24

Date Validation using regex

0 Answers0