[thelist] Page Contruction, HTTP Connections and Page Load Ti me (semi long)

Kowalkowski, Lee (ASPIRE) lee.kowalkowski at hmrcaspire.com
Tue Nov 22 03:42:24 CST 2005


> -----Original Message-----
> Tom Dell'Aringa wrote:
>
> Statement: A browser holds open one and only one connection 
> while loading the contents of the
> HEAD element. It cannot use multiple connections until these 
> items have fully loaded. Thus, the
> more you have in the HEAD, the worse performance you can expect.
> 

STOP!  This is surely a reference to the HTTP HEAD method, not the HEAD
element of your HTML document.  The browser only uses one connection for
HTTP HEAD because it's not possible to specify portions, because until it
has had a HTTP HEAD response, it will not know the Content Length.  

When the browser subsequently performs a HTTP GET, it can use many
connections by performing partial GETs and specifying byte ranges.

So, when a browser fetches your HTML Document, it can use as many
connections as it likes (although I don't know if any browsers do).  

However, a reference to an undeferred script file will interrupt the parsing
of a HTML document, because the script may generate more document content,
which may need to be parsed immediately after script execution  (e.g.
document.write statements).  

Therefore, each script file must be loaded & executed before document
parsing continues, subsequent references to other scripts will be as yet
unparsed, so it cannot be expected to request them.   A browser may use many
connections to fetch one script file (although I don't know if any browsers
do).

- LK


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