//Valiates form submission
function validate(form){
if(notEmpty(form.firstname)){
  if(notEmpty(form.lastname)){
    if(notEmpty(form.email)){
      if(notEmpty(form.phone)) {
      return true;
      }
    }
  }
}
return false;
}
//checks that fields are filled
function notEmpty(elem){
  var str = elem.value;
  if(str.length == 0){
    alert("You must fill in all required fields (*)");
    return false;
  }
  else {
    return true;
  }
}