twitter-scroll.js

var latestTweetIndex = 0;

function scrollToNextElement(e) {
  if(e.keyCode == 32 && e.target == document.body) {
    e.preventDefault();
    var streamItems = document.querySelectorAll('.stream-items>.stream-item');
    console.log('streamItems', streamItems.length);
    latestTweetIndex = findLatestVisibleTweetIndex(streamItems);
    console.log('latestTweetIndex--', latestTweetIndex);
    window.scrollBy(0, streamItems[latestTweetIndex].getBoundingClientRect().bottom - (window.innerHeight || document.documentElement.clientHeight));
  }
}

function isElementInViewport (el) {
  if (typeof jQuery === "function" && el instanceof jQuery) {
    el = el[0];
  }
  var rect = el.getBoundingClientRect();
  return (
    rect.top >= 0 &&
    rect.left >= 0 &&
    rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) && /*or $(window).height() */
    rect.right <= (window.innerWidth || document.documentElement.clientWidth) /*or $(window).width() */
  );
}


function findLatestVisibleTweetIndex(streamItems) {
  for (var i=latestTweetIndex; i < streamItems.length; i++) {
    if(!isElementInViewport(streamItems[i]) && i>latestTweetIndex) {
      return i;
    }
  }
  return latestTweetIndex;
}


window.addEventListener('keydown', scrollToNextElement);