Form validation

HTML

<div id="error"></div>

<form id="idCheck">
    <p>Enter the ID Number: <input id="idnumber" /> </p>
    <p> <input type="submit" value="Check" /> </p>
</form>

<div id="result"> </div>

CSS

#error {
    color: red;
    border: 1px solid red;
    padding: 5px;
    display: none;
}

#result {
    padding: 20px;
}

p {
    display: block;
    text-align: right;
}

input, select {
    width: 100px;
}

JavaScript

function Validate() {
    // first clear any left over error messages
    $('#error p').remove();

    // store the error div, to save typing
    var error = $('#error');

    var idNumber = $('#idnumber').val();


    // assume everything is correct and if it later turns out not to be, just set this to false
    var correct = true;

    //Ref: http://www.sadev.co.za/content/what-south-african-id-number-made
    // SA ID Number have to be 13 digits, so check the length
    if (idNumber.length != 13 || !isNumber(idNumber)) {
        error.append('<p>ID number does not appear to be authentic - input not a valid number</p>');
        correct = false;
    }

    // get first 6 digits as a valid date
    var tempDate = new Date(idNumber.substring(0, 2), idNumber.substring(2, 4) - 1, idNumber.substring(4, 6));

    var id_date = tempDate.getDate();
    var id_month = tempDate.getMonth();
    var id_year = tempDate.getFullYear();

    var fullDate = id_date + "-" + id_month + 1 + "-" + id_year;

    if (!((tempDate.getYear() == idNumber.substring(0, 2)) && (id_month == idNumber.substring(2, 4) - 1) && (id_date == idNumber.substring(4, 6)))) {
        error.append('<p>ID number does not appear to be authentic - date part not valid</p>');
        correct = false;
    }

    // get the gender
    var genderCode = idNumber.substring(6, 10);
    var gender = parseInt(genderCode) < 5000 ? "Female" : "Male";

    // get country ID for citzenship
    var citzenship = parseInt(idNumber.substring(10, 11)) == 0 ? "Yes" : "No";

    // apply Luhn formula for check-digits
    var tempTotal = 0;
    var checkSum = 0;
    var multiplier = 1;
    for (var i = 0; i < 13; ++i) {
        tempTotal = parseInt(idNumber.charAt(i)) * multiplier;
        if (tempTotal > 9) {
            tempTotal = parseInt(tempTotal.toString().charAt(0)) + parseInt(tempTotal.toString().charAt(1));
        }
        checkSum = checkSum + tempTotal;
        multiplier = (multiplier % 2 == 0) ? 1 : 2;
    }
   ...