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POChrome performance: "standard" property names vs. non-standard
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  1. POChrome performance: "standard" property names vs. non-standard
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    copied!<p>So this is an interesting one... While I was testing the performance of setAttribute vs. normal property set on an element, I found an odd behavior, which I then tested on regular objects and... It's still odd!</p> <p>So if you have an object <code>A = {}</code>, and you set its property like <code>A['abc_def'] = 1</code>, or <code>A.abc_def = 1</code>, they are basically the same. But then if you do <code>A['abc-def']</code> = 1 or <code>A['123-def']</code> = 1 then you are in trouble. It goes wayyy slower. I set up a test here: <a href="http://jsfiddle.net/naPYL/1/" rel="nofollow">http://jsfiddle.net/naPYL/1/</a>. They all work the same on all browsers except chrome. The funny thing is that for "abc_def" property, chrome is actually much faster than Firefox and IE, as I expected. But for "abc-def" it's at least twice as slow.</p> <p>So what happens here basically (at least from my tests) is that when using "correct" syntax for properties (legal C syntax, which you can use with dot properties) - It's fast, but when you use syntax that requires using brackets (a[...]) then you're in trouble.</p> <p>I tried to imagine what implementation detail would distinguish in such a way between the two modes, and couldn't. Because as I think of it, if you do support those non-standard names, you are probably translating all names to the same mechanics, and the rest is just syntax which is compiled into that mechanic. So . syntax and [] should be all the same after compilation. But obviously something is going the other way around here...</p> <p>Without looking at V8's source code, could anyone think of a really satisfying answer? (Think of it as an exercise :-))</p> <p><a href="http://jsperf.com/property-dash-parformance" rel="nofollow">Here's also a quick jsperf.com example</a></p> <p>Thanks to NDM for the jsperf example!</p> <blockquote> <p><strong>Edit:</strong></p> <p>To clarify, of course I want also a concrete answer from the real code (which I already found) or to be more precise - the reason behind that specific implementation. That is one of the reasons I asked you to look at it "as an exercise", to look behind the technical implementation and try to find the reason.</p> <p>But I also wanted to see how other people's minds work in cases like these. This may sound "vague" to some of you - but it is very useful to try and think like other people from time to time, or take their point of view. It enhances your own ways of thinking.</p> </blockquote>
 

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