title: crawl dynamic data using scrapy
body: <p>I try to get the product rating information from target.com. The URL for the product is </p>
  
  <p><a href="http://www.target.com/p/bounty-select-a-size-paper-towels-white-8-huge-rolls/-/A-15258543#prodSlot=medium_1_4&amp;term=bounty" rel="nofollow">http://www.target.com/p/bounty-select-a-size-paper-towels-white-8-huge-rolls/-/A-15258543#prodSlot=medium_1_4&amp;term=bounty</a></p>
  
  <p>After looking through response.body, I find out that the rating information is not statically loaded. So I need to get using other ways. I find some similar questions saying in order to get dynamic data, I need to</p>
  
  <ol>
  <li>find out the correct XHR and where to send request</li>
  <li>use FormRequest to get the right json</li>
  <li>parse json
  (if I am wrong about the steps please tell me)</li>
  </ol>
  
  <p>I am stuck at step 2 right now, i find out that one XHR named 15258543 contained rating distribution, but I don't know how can I sent a request to get the json. Like to where and use what parameter.</p>
  
  <p>Can someone can walk me through this?
  Thank you!</p>