But why's the browser DOM still so slow after 10 years of effort?

user_257493 0
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The web browser DOM has been around since the late '90s, but it remains one of the largest constraints in performance/speed.

We have some of the world's most brilliant minds from Google, Mozilla, Microsoft, Opera, W3C, and various other organizations working on web technologies for all of us, so obviously this isn't a simple "Oh, we didn't optimize it" issue.

My question is if i were to work on the the part of a web browser that deals specifically with this, why would I have such a hard time making it run faster?

My question is not asking what makes it slow, it's asking why hasn't it become faster?

This seems to be against the grain of what's going on elsewhere, such as JS engines with performance near that of C++ code.

Example of quick script:

for (var i=0;i<=10000;i++){
    someString = "foo";
}

Example of slow because of DOM:

for (var i=0;i<=10000;i++){
    element.innerHTML = "foo";
}

Some details as per request:

After bench marking, it looks like it's not an unsolvable slow issue, but often the wrong tool is used, and the tool used depends on what you're doing cross-browser.

It looks like the DOM efficiency varies greatly between browsers, but my original presumption that the dom is slow and unsolvable seems to be wrong.

I ran tests against Chrome, FF4, and IE 5-9, you can see the operations per second in this chart:

enter image description here

Chrome is lightning fast when you use the DOM API, but vastly slower using the .innerHTML operator (by a magnitude 1000-fold slower), however, FF is worse than Chrome in some areas (for instance, the append test is much slower than Chrome), but the InnerHTML test runs much faster than chrome.

IE seems to actually be getting worse at using DOM append and better at innerHTML as you progress through versions since 5.5 (ie, 73ops/sec in IE8 now at 51 ops/sec in IE9).

I have the test page over here:

http://jsperf.com/browser-dom-speed-tests2

What's interesting is that it seems different browsers seem to all be having different challenges when generating the DOM. Why is there such disparity here?

dom javascript
4 Answers

Actually, innerHTML is less slow than createElement.

In an effort to optimize I found js can parse enormous json effortlessly. Json parsers can have a huge number of nested function calls without issues. One can toggle between display:none and display:block thousands of elements without issues.

But if you try create a few thousand elements (or even if you simply clone them) performance is terrible. You don't even have to add them to the document!

Then, when they are created, insert and remove from the page works supper fast again.

It looks to me like the slowness has little to do with their relation to other elements of the page.

user_34441120
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