My question is can I change this code using variables and use conditionals and how can I do it? My problem is The Validation I need that it is only necessary to fill in only one piece of information and it is not necessary to fill out the entire form

 <script>

   function save_producto(){
   let fd=new FormData();

these are the values I want to pass to variables

    fd.append('arriba',document.getElementById('arriba').value);
    fd.append('abajo',document.getElementById('abajo').value);
    fd.append('imagen',document.getElementById('imagen').files[0]);

   

This the part show the errors

 
    request.open('POST','api/producto_save.php',true);
      request.onload=function(){
        if (request.readyState== 4 && request.status== 200) {
        let response= JSON.parse(request.responseText);
        console.log(response);

          if(response.state){
          alert("correcto");
          }else{
          alert(response.detail);
  }

  
}
}

send everything

request.send(fd);

}
</script>