How to increase the speed of AJAX

Although it seems that it gets heavier as you use AJAX, there seems to be a method of how to speed up properly.
Vivek Jishtu live and kickin ': Speed ​​up your AJAX based webapps

The first plan is to first set JavaScript as an external file. This prevents it from being read each time. It is because it enters the browser's cache. However, with this method, even if the new JavaScript is modified, the browser may not update the cached file in some cases.

In order to prevent such a situation,

Script src = "getjs.php? File = test1 & version = 0.1"
Script src = "getjs.aspx? File = test2 & amp; version = 0.2"

It is good to just divide the reference destination in such a way that it is a solution to that.

In addition, an example of custom is posted on the quote origin site so that the transfer speed of the server may be delayed. It seems to be quite effective, but how about the actual situation?