// common validators
// validates that the field value string has one or more characters in it
function isNotEmpty(elem) {
    var str = elem.value;
    if(str == null || str.length == 0) {
        alert("Please fill in the required field.");
        return false;
    } else {
        return true;
    }
}
   
// validates that the entry is a positive or negative number
function isNumber(elem) {
    var str = elem.value;
    var oneDecimal = false;
    var oneChar = 0;
    // make sure value hasn't cast to a number data type
    str = str.toString( );
    for (var i = 0; i < str.length; i++) {
        oneChar = str.charAt(i).charCodeAt(0);
        // OK for minus sign as first character
        if (oneChar == 45) {
            if (i == 0) {
                continue;
            } else {
                alert("Only the first character may be a minus sign.");
                return false;
            }
        }
        // OK for one decimal point
        if (oneChar == 46) {
            if (!oneDecimal) {
                oneDecimal = true;
                continue;
            } else {
                alert("Only one decimal is allowed in a number.");
                return false;
            }
        }
        // characters outside of 0 through 9 not OK
        if (oneChar < 48 || oneChar > 57) {
            alert("Enter only numbers into the field.");
            return false;
        }
    }
    return true;
}
   
// validates that the entry is 16 characters long
function isLen16(elem) {
    var str = elem.value;
    if (str.length != 16) {
        alert("Entry does not contain the required 16 characters.");
        return false;
    } else {
        return true;
    }
}
   
// validates that the entry is formatted as an email address
function isEMailAddr(elem) {
    var str = elem.value;
    str = str.toLowerCase( );
    if (str.indexOf("@") > 1) {
        var addr = str.substring(0, str.indexOf("@"));
        var domain = str.substring(str.indexOf("@") + 1, str.length);
        // at least one top level domain required
        if (domain.indexOf(".") == -1) {
            alert("Verify the domain portion of the email address.");
            return false;
        }
        // parse address portion first, character by character
        for (var i = 0; i < addr.length; i++) {
            oneChar = addr.charAt(i).charCodeAt(0);
            // dot or hyphen not allowed in first position; dot in last
            if ((i == 0 && (oneChar == 45 || oneChar == 46))  || 
                (i == addr.length - 1 && oneChar == 46)) {
                alert("Verify the user name portion of the email address.");
                return false;
            }
            // acceptable characters (- . _ 0-9 a-z)
            if (oneChar == 45 || oneChar == 46 || oneChar == 95 || 
                (oneChar > 47 && oneChar < 58) || (oneChar > 96 && oneChar < 123)) {
                continue;
            } else {
                alert("Verify the user name portion of the email address.");
                return false;
            }
        }
        for (i = 0; i < domain.length; i++) {
            oneChar = domain.charAt(i).charCodeAt(0);
            if ((i == 0 && (oneChar == 45 || oneChar == 46)) || 
                ((i == domain.length - 1  || i == domain.length - 2) && oneChar == 46)) {
                alert("Verify the domain portion of the email address.");
                return false;
            }
            if (oneChar == 45 || oneChar == 46 || oneChar == 95 || 
                (oneChar > 47 && oneChar < 58) || (oneChar > 96 && oneChar < 123)) {
                continue;
            } else {
                alert("Verify the domain portion of the email address.");
                return false;
            }
        }
        return true;
    }
    alert("The email address may not be formatted correctly. Please verify.");
    return false;
}