Deprecating the unload event about infinite-scroll HOT 2 OPEN

proto.onVisibilityChange = function() {
  if (!this.scrollPage) return;
  if (this.scrollPage.top === 0) return;
  if (document.visibilityState === 'visible') return;

  // calculate where scroll position would be on refresh
  let scrollY = window.scrollY - this.scrollPage.top + this.top;
  // disable scroll event before setting scroll #679
  this.destroyHistory();
  scrollTo(0, scrollY);
};

proto.bindVisibilityChangeEvent = function(isBind) {
  let addRemove = isBind ? 'addEventListener' : 'removeEventListener';
  window[addRemove]('visibilitychange', this.onVisibilityChange);
};

proto.createHistoryAppend = function() {
  this.updateMeasurements();
  this.updateScroller();
  // array of scroll positions of appended pages
  this.scrollPages = [
    // first page
    {
      top: 0,
      path: location.href,
      title: document.title,
    },
  ];
  this.scrollPage = this.scrollPages[0];
  // events
  this.scrollHistoryHandler = this.onScrollHistory.bind( this );
  this.visibilityChangeHandler = this.onVisibilityChange.bind(this);
  this.scroller.addEventListener( 'scroll', this.scrollHistoryHandler );
  this.on( 'append', this.onAppendHistory );
  this.bindHistoryAppendEvents( true );
  this.bindVisibilityChangeEvent(true);
};

proto.bindHistoryAppendEvents = function(isBind) {
  let addRemove = isBind ? 'addEventListener' : 'removeEventListener';
  this.scroller[addRemove]('scroll', this.scrollHistoryHandler);
  this.bindVisibilityChangeEvent(isBind);
};