Two common scenarios where scripts aren't put at the bottom:
- Having talked to web devs across hundreds of companies it's often
the case that they control a certain section of the page. Inserting
content outside of that section requires changing so much
infrastructure, they skip the optimization.
- 3rd parties have no control over where their snippet is placed in
the content owner's page. Providing a snippet that contains "DEFER" will
guarantee they don't block the main page's content.
-Steve
On 2/10/2010 1:31 AM, Henri Sivonen wrote:
On Feb 8, 2010, at 23:54, Steve Souders wrote:
It would be good to mention this optional behavior here, something along the
lines of browsers may want to do speculative parsing, but shouldn't create DOM
elements, etc. - only kickoff HTTP requests.
FWIW, the HTML5 parser in Gecko (not on by default yet) does more than just
kicks off HTTP requests. However, what it does isn't supposed to be detectable
by author-supplied scripts.
4. "If the element has a src attribute, [snip] the specified resource must then be
fetched, from the origin of the element's Document."
If the script has DEFER, the request should not start until after parsing
is finished. Starting it earlier could block other (non-deferred) requests due
to a connection limit or limited bandwidth.
As I understand it, starting the request early is the whole point of 'defer'.
Otherwise, the author could put those scripts at the end of the page.
