Responsible JavaScript

Simon Hearne’s Request Map Generator (http://bkaprt.com/rjs39/07-12) finds all the unique origins involved for a given web page. You can also use the Domains tab in WebPageTest to do this. With this information, you can establish connections as early as possible using the preconnect resource hint, which we covered in Chapter 4. If you can avoid some of the latency involved in these request chains, that’s a big performance win.