$(document).ready(function() {
    $('#join-form').submit(validate);

    $("#join-first, #join-last, #join-email, #join-zip").defaultvalue(
        "First name",
        "Last name",
        "Email",
        "Zip code"
    );
  
});

function validate() {
  
  if ( 
    $("#join-first").val() == "First name" || 
    $("#join-first").val() == "" ||
    $("#join-last").val() == "Last name" || 
    $("#join-last").val() == "" ||
    $("#join-email").val() == "Email" ||
    ! /^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}$/.test( $("#join-email").val() ) || 
    $("join-zip").val() == "Zip code" ||
    $("join-zip").val() == "" ) {
      alert('Please provide your name, email address and zip code to subscribe');
    return false;
  } else {
    return true;
  }
}