I want to make a "Previous" Button

Customization
1 
const next = document.getElementById("next");
  const ob = ["view_3", "view_5", "view_4", "view_5", "view_6", "view_2"];
  var clickCount = 0;
  next.addEventListener("click", function () {
    const index = clickCount % ob.length;

    while (true) {
      viewer.switchToView(ob[index]);
      break;
    }
    clickCount++;
  });