code: function(node) {
          node = $(node);
  
          var container = this.container,
              threshold = this.options.threshold,
              conHeight = container.height(),
              conWidth = container.width(),
              scrollTop = container.scrollTop(),
              scrollLeft = container.scrollLeft(),
              nodeOffset = node.offset(),
              left = nodeOffset.left,
              top = nodeOffset.top;
  
          // Re-adjust the offset to match the parent container
          // is() fails when checking against window
          if (container[0] !== window) {
              var conOffset = container.offset();
  
              left -= conOffset.left;
              top -= conOffset.top;
          }
  
          return (
              // Element is not hidden
              node.is(':visible') &&
              // Below the top
              (top >= (scrollTop - threshold)) &&
              // Above the bottom
              (top <= (scrollTop + conHeight + threshold)) &&
              // Right of the left
              (left >= (scrollLeft - threshold)) &&
              // Left of the right
              (left <= (scrollLeft + conWidth + threshold))
          );
      }
docs: Verify that the item is within the current browser viewport.
  
  @param {jQuery} node
  @returns {bool}