jquery validation

simple-validation.js

var form = $('.application-form'),
	requiredFields = $('.required', form),
	email_pattern = /^\w+@[a-zA-Z_]+?\.[a-zA-Z]{2,3}$/,
	key_range = /4[8-9]|5[0-7]|45|32|13/,
	topmost_error = $('.application-form-placeholder').offset().top;
	has_error = true,

$('#applicant-birthdate').datepicker({
	changeMonth: true,
	changeYear: true,
	showOtherMonths: true
});

$('.number', form).on('keypress', function(e) {
	if (!key_range.test(e.keyCode)) {
		return false;
	}
});

form.submit(function(e) {

	$('.error', form).removeClass('error');
	$('.error-message', form).empty();

	has_empty = has_empty_fields(requiredFields.filter('[type=text], .multi-input'));
	valid_email = is_email_valid(requiredFields.filter('[name=email-contact]'));

	has_error = has_empty || !valid_email;

	if (has_error || !is_certified() || !is_read()) {
		$(window).scrollTop(topmost_error);
		e.preventDefault();
	}



});

function has_empty_fields(list_of_required_fields) {
	// check if form has empty textfields

	// initialize empty text field array holder
	var empty_fields;

	// check each text field
	$.each(list_of_required_fields, function(i, el) {

		if ($(el).is('input')) {
			// do this if element is a textfield

			// get value of the textfield
			var field = $(el),
				field_value = field.val();

			// verify if the content of the textfield is empty
			if (field_value == "" || field_value == null || !field_value) {
				// if empty push element to array holder
				field.addClass('error');
			}
			
		} else {
			// else assume checkbox/radio
			var field = $('input', el);

			// check if checked
			if (!is_checked(field)) {
				$(el).addClass('error');
			}

		}


	});

	// get erronoues fields
	empty_fields = list_of_required_fields.filter('.error');

	// display error if there is an empty field
	if (empty_fields.length) {
		$('.error-message', form).append($("<p/>").text("* fields in boxes are required"));
	}

	return !!empty_fields.length;
	
}


function is_email_valid(email_field) {
	// this function will validate format of email address

	var field = $(email_field),
		field_value = field.val(),
		blank_field_value = (!field_value || field_value == "" || field_value == null),
		email_correct_format = email_pattern.test(field_value);
	
		if (!blank_field_value && !email_correct_format) {
		email_field.addClass('error');
		$('.error-message', form).append($("<p/>").text("* not a valid email address format"));
	}

	return email_correct_format;

}


function is_checked(el) {

	var checked = $(el).is(':checked')
	if (!checked) {
		$(el).parents("label").addClass('error');
	}

	return checked;

}

function is_certified() {
	var certified = is_checked('#certify');
	if (!certified) $('.error-message', form).append($("<p/>").text("* you must certify that the information stated are true and correct"));
	return certified;
}

function is_read() {
	var read = is_checked('#agree');
	if (!read) $('.error-message', form).append($("<p/>").text("* you must agree with the terms and condition"));
	return read;
}