$('#register_button').click(function(e){
 
      if ($('#register_firstname').val().length ==0 ||
      $('#register_lastname').val().length ==0 ||
      $('#register_email').val().length ==0){
          alert ('Todos los campos son obligatorios');
            return false;
      }
 
});

{# Participants first name #}
        <div class='{{ aSurveyInfo.class.registerformcolrow }} form-group row' {{ aSurveyInfo.attr.registerformcolrow }}>
            <label for='register_firstname' class='{{ aSurveyInfo.class.registerformcolrowlabel }} control-label '>{{ gT("First name:") }}</label>
            <div class="">
                {{ C.Html.textField('register_firstname', aSurveyInfo.sFirstName, ({'id' : 'register_firstname','class' : 'form-control'})) }}
            </div>
        </div>
 
        {# Participants last name #}
        <div class='{{ aSurveyInfo.class.registerformcolrowb }} form-group row' {{ aSurveyInfo.attr.registerformcolrowb }}>
            <label {{ aSurveyInfo.attr.registerformcolrowblabel }}  class='{{ aSurveyInfo.class.registerformcolrowblabel }} control-label '>{{ gT("Last name:") }}</label>
            <div {{ aSurveyInfo.attr.registerformcolrowbdiv }} >
                {{ C.Html.textField('register_lastname', aSurveyInfo.sLastName, ({'id' : 'register_lastname', 'class' : 'form-control'})) }}
            </div>
        </div>
 
        {# Participants email #}
        <div class='{{ aSurveyInfo.class.registerformcolrowc }} form-group row' {{ aSurveyInfo.attr.registerformcolrowc }}>
            <label {{ aSurveyInfo.attr.registerformcolrowclabel }} class='{{ aSurveyInfo.class.registerformcolrowclabel }}  control-label'> {{ gT("Email address:") }} {{ include('./subviews/registration/required.twig') }}</label>
            <div {{ aSurveyInfo.attr.registerformcolrowcdiv }}  >
                {{ C.Html.textField('register_email', aSurveyInfo.sEmail, ({'id' : 'register_email','class' : 'form-control input-sm','required' : true})) }}
            </div>
        </div>

{# Participants first name #}
        <div class='{{ aSurveyInfo.class.registerformcolrow }} form-group row' {{ aSurveyInfo.attr.registerformcolrow }}>
            <label for='register_firstname' class='{{ aSurveyInfo.class.registerformcolrowlabel }} control-label '>{{ gT("First name:") }} {{ include('./subviews/registration/required.twig') }}</label>
            <div class="">
                {{ C.Html.textField('register_firstname', aSurveyInfo.sFirstName, ({'id' : 'register_firstname','class' : 'form-control','required' : true})) }}
            </div>
        </div>
 
        {# Participants last name #}
        <div class='{{ aSurveyInfo.class.registerformcolrowb }} form-group row' {{ aSurveyInfo.attr.registerformcolrowb }}>
            <label {{ aSurveyInfo.attr.registerformcolrowblabel }}  class='{{ aSurveyInfo.class.registerformcolrowblabel }} control-label '>{{ gT("Last name:") }} {{ include('./subviews/registration/required.twig') }}</label>
            <div {{ aSurveyInfo.attr.registerformcolrowbdiv }} >
                {{ C.Html.textField('register_lastname', aSurveyInfo.sLastName, ({'id' : 'register_lastname', 'class' : 'form-control','required' : true})) }}
            </div>
        </div>
 
        {# Participants email #}
        <div class='{{ aSurveyInfo.class.registerformcolrowc }} form-group row' {{ aSurveyInfo.attr.registerformcolrowc }}>
            <label {{ aSurveyInfo.attr.registerformcolrowclabel }} class='{{ aSurveyInfo.class.registerformcolrowclabel }}  control-label'> {{ gT("Email address:") }} {{ include('./subviews/registration/required.twig') }}</label>
            <div {{ aSurveyInfo.attr.registerformcolrowcdiv }}  >
                {{ C.Html.textField('register_email', aSurveyInfo.sEmail, ({'id' : 'register_email','class' : 'form-control input-sm','required' : true})) }}
            </div>
        </div>