Need to check the value of the uploaded file while updating a form

if(doc.value[i].file == Blob)
    formData.append("docs[]", doc.value[i].file , doc.value[i].file.name );
  
  else
    formData.append("docs2[]", docs.value[i].file);

Need to update a form if new files not uploaded then i need to attach the old uploaded file details (object) to formbuilder