}\n\n  _getScrollHeight() {\n    return this._scrollElement.scrollHeight || Math.max(\n      document.body.scrollHeight,\n      document.documentElement.scrollHeight\n    )\n  }\n\n  _getOffsetHeight() {\n    return this._scrollElement === window ?\n      window.innerHeight : this._scrollElement.getBoundingClientRect().height\n  }\n\n  _process() {\n    const scrollTop = this._getScrollTop() + this._config.offset\n    const scrollHeight = this._getScrollHeight()\n    const maxScroll = this._config.offset...