code: function (pageNum) {
              var index = util.clamp(pageNum - 1, 0, this.numPages - 1),
                  page = this.state.pages[index];
              return { top: page.y0, left: page.x0 };
          }
docs: Given a page number, return an object with top and left properties
  of the scroll position for that page
  @param   {int} pageNum The page number
  @returns {Object}      The scroll position object