Why is there a delay before chrome Console network requests?

  node.js, question

Address:

https://developers.google.com …

As shown in the figure:
clipboard.png

Question 1: There is a red line under the request, that is, there is a gap between the fifth request and the sixth request, that is, there is a gap between the end of the fifth request and the beginning of the sixth request. Why

Question 2: In our projects, some requests are synchronous and some are asynchronous. For example, the second and third requests start at the same time. May I know which are synchronous and which are asynchronous in our daily projects?

I’d like to thank you very much if you can dispel my doubts.

The browser loading js will block the page.
PointXHRThe requests are all asynchronous.