Question

PageSpeed and Yslow suggest that to combine javascripts file to reduce HTTPRequest. But this is becuase (I think) pre ie8 browser has no more than 2 serverhost connection.

But nowaday, browser has 6 serverhost connections, which means it has download javascripts in parrallel. So let say we have 1MB of javascript, should we break it down into 6 different files in similar size to obtain max download speed? Please let me know.

Micahel.S

Answer 1

The answer to your question is no. However, assuming you are able to serve your content in a completely isolated environment where only IE8 is used (like company intranet), then the answer to your question becomes: no.

Since you aren’t designing for IE6-7 I assume you are in an isolated environment (otherwise you are making a poor designing decision). In this environment, yes you might see small benefits from breaking down JavaScript files, but I recommend against it.

Why? Since you are optimizing for speed, I assume you are putting JavaScript at the bottom of the body tag in your HTML document, in order to prevent JS from blocking download of DOM. This is a fundamental practice to make the page appear to be loading faster. However, by placing the content in the bottom of the body, your question becomes moot. Since the DOM is no longer being blocked by the script tags, whatever speed benefits you could achieve by using parallel downloading would be lost on the user because they see the page load before the browser even requests the JavaScript files.

tl;dr: There is no practical speed advantage to break JS into multiple files for parallel downloading.