code: function openPopup(params) {
    var container = getContainer();
    var popup = getPopup();
  
    if (params.onBeforeOpen !== null && typeof params.onBeforeOpen === 'function') {
      params.onBeforeOpen(popup);
    }
  
    if (params.animation) {
      addClass(popup, swalClasses.show);
      addClass(container, swalClasses.fade);
      removeClass(popup, swalClasses.hide);
    } else {
      removeClass(popup, swalClasses.fade);
    }
  
    show(popup); // scrolling is 'hidden' until animation is done, after that 'auto'
  
    container.style.overflowY = 'hidden';
  
    if (animationEndEvent && !hasClass(popup, swalClasses.noanimation)) {
      popup.addEventListener(animationEndEvent, function swalCloseEventFinished() {
        popup.removeEventListener(animationEndEvent, swalCloseEventFinished);
        container.style.overflowY = 'auto';
      });
    } else {
      container.style.overflowY = 'auto';
    }
  
    addClass([document.documentElement, document.body, container], swalClasses.shown);
  
    if (params.heightAuto && params.backdrop && !params.toast) {
      addClass([document.documentElement, document.body], swalClasses['height-auto']);
    }
  
    if (isModal()) {
      fixScrollbar();
      iOSfix();
      IEfix();
      setAriaHidden(); // sweetalert2/issues/1247
  
      setTimeout(function () {
        container.scrollTop = 0;
      });
    }
  
    if (!isToast() && !globalState.previousActiveElement) {
      globalState.previousActiveElement = document.activeElement;
    }
  
    if (params.onOpen !== null && typeof params.onOpen === 'function') {
      setTimeout(function () {
        params.onOpen(popup);
      });
    }
  }
docs: Open popup, add necessary classes and styles, fix scrollbar
  
  @param {Array} params