On Feb 12, 2010, at 8:29 AM, Boris Zbarsky wrote:
Test 1: ~4350ms
Test 2: ~2100ms
Test 3: ~80ms
Test 4: ~10ms
and in Opera 10.5 pre alpha:
Test 1: ~520ms
Test 2: ~3809ms
Test 3: ~541ms
Test 4: ~3828ms
and in Safari 4:
Test 1: ~260ms
Test 2: ~1309ms
Test 3: ~131ms (?)
Test 4: ~20ms
Given that webkit doesn't cache the nodelist, I'm not sure how to
explain the Safari numbers; perhaps Maciej can do that.
We cache the "guts" of the NodeList, so we save all the tree walking
and a chunk of the object creation cost in the case where caching is
possible. More specifically, we save some of the C++ level allocations
but not the JS-level allocations, and GC allocation is pretty
expensive. As you can see, that still doesn't get us as fast as
Mozilla's full caching, even though we are faster in the uncached case.
Philip Taylor also discovered that doing getElementsByTagName in a
loop is a reasonably common pattern, here are some real-world examples
he cited:
http://www.hotelgoal.com/city/vn/hotel-in-bai-chay.htm
for(i=0; i< document.getElementById(frm).getElementsByTagName
('SELECT').length; i++){
if(document.getElementById(frm).getElementsByTagName('SELECT')
[i].value==0){
http://www.esiweb.org/index.php?lang=fr&id=280&portrait_ID=66&function=print
while (document.getElementsByTagName("span")[i] != null) {
if (document.getElementsByTagName("span")[i].className
== "fn") {
http://google.com/codesearch?q=getElementsByTagName%5C%28%5B%5E%29%5D%2B%5C%29%5C%5B%5Ba-zA-Z%5D
Regards,
Maciej
