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POJavascript, IE, Strings, and Performance problems
 

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    <p>So we have this product, and it's really slow in IE. We've already applied a lot of the practices advised by the IE guys themselves (<a href="http://blogs.msdn.com/ie/archive/2006/08/28/728654.aspx" rel="nofollow noreferrer">like this</a>, and <a href="http://blogs.msdn.com/ie/archive/2007/01/04/ie-jscript-performance-recommendations-part-3-javascript-code-inefficiencies.aspx" rel="nofollow noreferrer">this</a>), and try to sacrifice clean code for performance in the critical parts like DOM manipulation.</p> <p>However, as you can see in this IE profiler screenshot.. <a href="http://i43.tinypic.com/24g57c1.png" rel="nofollow noreferrer">alt text http://i43.tinypic.com/24g57c1.png</a></p> <p>Just "String" is the biggest offender. Almost 750ms of exclusive time.</p> <p>Does this mean IE is spending 750ms just instantiating Strings? I also read this stuff on the <a href="http://dev.opera.com/articles/view/javascript-best-practices/" rel="nofollow noreferrer">Opera dev blog</a>:</p> <blockquote> <p>A build script can remove whitespace, comments, replace strings with Array lookups (to avoid MSIE creating a string object for every single instance of a string — even in conditions)</p> </blockquote> <p>But no more info regarding this. Anyone can clarify? It seems like IE has to create a full String instance every time you have " " in your code, which could explain this, but I don't know what the array lookup optimization would look like. BTW- we don't really do much of string concatenation anywhere in the code.</p> <p>The library we use is MooTools 1.2.4 </p> <p>Any suggestions will be appreciated! Thx</p> <p>UPDATE- I'm particularly interested in the tip mentioned above about "array lookup optimization". Our library is big (1MB) so it has a lot of strings in it, like any other JS code. But since our library is bigger than most, these Strings are actually causing speed issues. </p> <p>Also, does anybody know if adding stuff to the String.prototype makes every instance slower?</p>
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