method of judging amd may cause error：Cannot set property 'Swipe' of undefined

[postbird]

Error in：

  if (typeof define === 'function' && define.amd) {
    // AMD. Register as an anonymous module.
    // eslint-disable-next-line no-undef
    define([], function () {
      root.Swipe = factory(); // Cannot set property 'Swipe' of undefined
      return root.Swipe;
    });

somtimes, judgement of define and define.amd may be true, but can not promise that this is an object, it may be undefined, then there will be an error.

suggestion like ：

root = root || {} ; // make sure that  root is an object