text: let id = (id) => document.getElementById(id);
  let classes = (classes) => document.getElementsByClassName(classes);
  let username = id("username"),
      email = id("email"),
      password = id("password"),
      form = id("form"),
      errorMsg = classes("error"),
      successIcon = classes("success-icon"),
      failureIcon = classes("failure-icon");
  
  form.addEventListener("submit", (e) => {
      e.preventDefault();
  
      engine(username, 0, "Username cannot be blank");
      engine(email, 1, "Email cannot be blank");
      engine(password, 2, "Password cannot be blank");
  });
  
  let engine = (id, serial, message) => {
      if (id.value.trim() ===""){
          errorMsg[serial].innerHTML = message;
          id.style.border = "2px solid red";
          failureIcon[serial].style.opacity ="1";
          successIcon[serial].style.opacity = "0";
      }
      else {
          errorMsg[serial].innerHTML = "";
          id.style.border = "2px solid green";
          failureIcon[serial].style.opacity = "0";
          successIcon[serial].style.opacity = "1";
      }
  }