JavaScript Performance: Fast DOM Iterator

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JavaScript Performance: Fast DOM Iterator

After numerous tests, this function provides the most performant way to iterate over all the elements in the DOM:

function walkTheDom() {

var items = document.getElementsByTagName("*");

var i=items.length;

var item;

{

item = items[i];

//Do something with item

}

while (--i);

}

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Print posted @ Thursday, March 02, 2006 4:13 AM

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# re: JavaScript Performance: Fast DOM Iterator

Interesting... can you elaborate on the different methods you tested and the times they took? 3/3/2006 7:51 AM | Patrick Fitzgerald

# re: JavaScript Performance: Fast DOM Iterator

Hey Patrick ... you can check out my test page here

http://michaelparsons.ca/javascriptperformance.htm
3/3/2006 8:32 AM | Mike Parsons

# re: JavaScript Performance: Fast DOM Iterator

You got a bug in the code - the first item is out of range. It should read item = items[i-1];

Otherwise: Thanks! 3/9/2008 9:15 AM | Johannes

# re: JavaScript Performance: Fast DOM Iterator

i--;
do {
item = items[i];
//Do something with item
}
while(i--);

also the expression in *while* must
be post-decrement instead,
otherwise you'll miss item[0].

cheers
2/26/2009 2:51 AM | Anonymous

# re: JavaScript Performance: Fast DOM Iterator

i just understood how it works when applying the suggestion of Johannes. in his fix it must stay pre-increment:

do {
item = items[i-1];
//Do something with item

}
while(--i);
2/26/2009 2:57 AM | Anonymous

# re: JavaScript Performance: Fast DOM Iterator

nice script and i think it's a little bit faster than normal flow. 5/24/2010 6:12 AM | Nirala

# clearer logic

Thanks for doing these benchmarks! I believe the clearest way to write the reverse loop is

while (i--) {
item = items[i];
// Do something with item
} 10/23/2010 9:37 PM | Katherine

# re: JavaScript Performance: Fast DOM Iterator

var i=items.length;
var item;
do
{
item = items[--i];
//Do something with item
}
while (i);

Though I wonder how much faster this'll be than a normal for loop. Could you post your test results? 2/16/2011 1:10 PM | Richard

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