Thanks Stephen! I gave your reply a 5 star rating because you deserve
it.
On Feb 24, 1:28 pm, Stephan Veigl <stephan.ve...@gmail.com> wrote:
> Hi,
>
> I've done some profiling on this, and $("p", $("#foo")) is faster than
> $("#foo p") in both jQuery 1.2.6 and 1.3.2.
>
> the test HTML consists of 100 <p>s in a "foo" <div> and 900 <p>s in a
> "bar" <div>.
>
> However the factor differs dramatically:
> In 1.2.6 the speedup from $("p", $("#foo")) to $("#foo p") was between
> 1.5x (FF) and 2x (IE),
> while for 1.3.2 the speedup is 20x (FF) and 15x (IE).
>
> $("p", $("#foo")) is faster in 1.3.2, by a factor of 1.5 (both FF and IE),
> while $("#foo p") is _slower_ in 1.3.2 by 8.5x (FF) and 4.6x (IE).
>
> Even with an empty "bar" div $("p", $("#foo")) is faster by a factor up to 3x.
>
> Conclusion:
> If you have an ID selector, first get the element by it's ID and use
> it as scope for further selects.
>
> by(e)
> Stephan
> 2009/2/23 ricardobeat <ricardob...@gmail.com>:
>
> > up to jQuery 1.2.6 that's how the selector engine worked (from the top
> > down/left to right). The approach used in Sizzle (bottom up/right to
> > left) has both benefits and downsides - it can be much faster on large
> > DOMs and some situations, but slower on short queries. I'm sure
> > someone can explain that in better detail.
>
> > Anyway, in modern browsers most of the work is being delegated to the
> > native querySelectorAll function, as so selector performance will
> > become more of a browser makers' concern.
>
> > - ricardo
>
> > On Feb 23, 1:08 pm, Peter Bengtsson <pete...@gmail.com> wrote:
> >> I watched the John Resig presentation too and learned that CSS
> >> selectors always work from right to left.
> >> That would mean that doing this::
>
> >> $('#foo p')
>
> >> Would extract all <p> tags and from that list subselect those who
> >> belong to #foo. Suppose you have 1000 <p> tags of them only 100 are
> >> inside #foo you'll have wasted 900 loops.
>
> >> Surely $('#foo') is the fastest lookup possible. Doing it this way
> >> will effectively limit the scope of the $('p') search and you will
> >> never be bothered about any <p> tags outside #foo.
>
> >> Or am I talking rubbish?
