code: function getOppositePlacement(placement) {
    const hash = { left: 'right', right: 'left', bottom: 'top', top: 'bottom' };
    return placement.replace(/left|right|bottom|top/g, matched => hash[matched]);
  }
docs: Get the opposite placement of the given one
  @method
  @memberof Popper.Utils
  @argument {String} placement
  @returns {String} flipped placement