$(function(){

    function validateForm(){
        // do something to return true (it's valid) or false (it's not valid)
        var fields = $('#form input[type=text]');

        for(var i = 0; i < fields.length; i++) {
            if(!validateField(fields.eq(i))){
                return false;
            }
        }
        return true;
    }

    function validateField($field) {
        if($field.data('required') && !validateRequire($field)) {
            return false;
        }
        if(+$field.data('min-length') && !validateMinLength($field, +$field.data('min-length'))) {
            return false;
        }
        if(+$field.data('max-length') && !validateMaxLength($field, +$field.data('max-length'))) {
            return false;
        }

        return true;
    }

    function validateRequire($field){
        return !!$field.val();
    }

    function validateMinLength($field, min){
        return $field.val().length >= min;
    }

    function validateMaxLength($field, max){
        return $field.val().length <= max;
    }

    $('#form').on('submit', function (event) {
        event.preventDefault();
        alert(validateForm()?'Форма валидна':'проверьте правильность формы');
    });

});