If ele on screen - js

if-el-onscreen.js

// A simple jQuery function to check if the element is visible on screen
// https://gist.github.com/agaase/6648737
$.fn.isOnScreen = function() {
  var win = $(window);
  var viewport = {
      top : win.scrollTop(),
      left : win.scrollLeft()
  };
  viewport.right = viewport.left + win.width();
  viewport.bottom = viewport.top + win.height();
  var bounds = this.offset();
  bounds.right = bounds.left + this.outerWidth();
  bounds.bottom = bounds.top + this.outerHeight();
  return (!(viewport.right < bounds.left || viewport.left > bounds.right || viewport.bottom < bounds.top || viewport.top > bounds.bottom));
};