Conditional logging is provided so that individual requests may be included or excluded from the logs based on characteristics of the request.
可以有选择地记录日志，从而能够根据请求的特征包含或从日志中删除单个请求。
2
Even if your components have a far future Expires header, a conditional GET request is still made whenever the user hits Reload or Refresh.
即使您的组件具有远的未来过期标头，一个条件GET请求仍付款时，用户点击Reload或刷新。
3
Listing 11 is best thought of as a giant conditional statement, which executes a particular branch based on the value of the o parameter in the request url.