Admin.js

$(document).ready(function () {
    $("form").submit(function (event) {
        $(".help-block").remove();
        var formData = {
            CarID : $("#CarID").val(),
            StartDate: $("#StartDate").val(),
            EndDate: $("#EndDate").val(),
            StateDate: $("#StateDate").val(),
        };
        // if Car ID is not Empty check if it is not a number
        if (isNaN(formData["CarID"])) {
            alert("Please enter a Valid Plate ID");
        }
        // if start date is not Empty
        if (formData["StartDate"] != "") {
            validatedate(formData["StartDate"]);
        }
        // if End date is not Empty
        if (formData["EndDate"] != "") {
            validatedate(formData["EndDate"]);
        }
        // if State date is not Empty
        if (formData["StateDate"]) {
            validatedate(formData["StateDate"]);
        }

        $.ajax({
            type: "POST",
            url: "Admin.php",
            data: formData,
            dataType: "json",
            encode: true,
        }).done(function (data) {
            console.log(data);
            if (!data.success) { // Error

                if (data.errors.email) { // If email already exists
                    $("#email-group").addClass("has-error");
                    $("#email-group").append('<div class="help-block">' + data.errors.email + "</div>");
                }

            } else { // Success
                $("form").html('<script></script>' + '<div class="alert alert-success">' + data.message + "</div>");
                window.location.href = '/Registration_and_Login/Welcome_page.php';
            }
        })
            .fail(function (data) {
                // $("#message-group").html('<div class="alert alert-danger">Could not reach server, please try again later.</div>');
            });
        event.preventDefault();

    });

});

//Check if the date is valid
function validatedate(dateString) {
    let dateformat = /^(0?[1-9]|1[0-2])[\/](0?[1-9]|[1-2][0-9]|3[01])[\/]\d{4}$/;

    // Match the date format through regular expression
    if (dateString.match(dateformat)) {
        let operator = dateString.split('/');

        // Extract the string into month, date and year
        let datepart = [];
        if (operator.length > 1) {
            pdatepart = dateString.split('/');
        }
        let month = parseInt(datepart[0]);
        let day = parseInt(datepart[1]);
        let year = parseInt(datepart[2]);

        // Create list of days of a month
        let ListofDays = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
        if (month == 1 || month > 2) {
            if (day > ListofDays[month - 1]) {
                ///This check is for Confirming that the date is not out of its range
                return false;
            }
        } else if (month == 2) {
            let leapYear = false;
            if ((!(year % 4) && year % 100) || !(year % 400)) {
                leapYear = true;
            }
            if ((leapYear == false) && (day >= 29)) {
                return false;
            } else if ((leapYear == true) && (day > 29)) {
                alert('Invalid date format!');
                return false;
            }
        }
    } else {
        alert("Invalid date format!");
        return false;
    }
    return true;
}