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POWhy does this javascript run so slow in IE when all it does is modify a select list?
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  1. POWhy does this javascript run so slow in IE when all it does is modify a select list?
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    copied!<p>I'm working on having a multi-select list where you can have items selected and then click an "Up" or "Down" button that will allow you to reorder those items within the list.</p> <p>I've got a simple self-contained example:</p> <pre><code>&lt;html&gt; &lt;head&gt; &lt;title&gt;Example&lt;/title&gt; &lt;script src="https://www.google.com/jsapi"&gt;&lt;/script&gt; &lt;script&gt; google.load('jquery', '1.4.1'); &lt;/script&gt; &lt;/head&gt; &lt;body&gt; &lt;select id="selectedDataPoints" multiple="multiple"&gt; &lt;option&gt;Pig&lt;/option&gt; &lt;option&gt;Duck&lt;/option&gt; &lt;option&gt;Dog&lt;/option&gt; &lt;option&gt;Zebra&lt;/option&gt; &lt;option&gt;Snake&lt;/option&gt; &lt;option&gt;Giraffe&lt;/option&gt; &lt;option&gt;Cow&lt;/option&gt; &lt;/select&gt; &lt;input type="button" id="btnReorderUp" value="Up" /&gt; &lt;input type="button" id="btnReorderDown" value="Down" /&gt; &lt;/body&gt; &lt;/html&gt; &lt;script type="text/javascript"&gt; var DataPointSelector = (function() { var $selectedList = $('#selectedDataPoints'); $('#btnReorderUp').click(function(e) { moveUp(); e.preventDefault(); }); $('#btnReorderDown').click(function(e) { moveDown(); e.preventDefault(); }); function moveUp() { var select = $selectedList[0]; for (var i = 1, n = select.options.length; i &lt; n; i++) if (select.options[i].selected &amp;&amp; !select.options[i - 1].selected) select.insertBefore(select.options[i], select.options[i - 1]); } function moveDown() { var select = $selectedList[0]; for (var i = select.options.length - 1; i &gt; 0; i--) if (select.options[i].selected &amp;&amp; !select.options[i + 1].selected) select.insertBefore(select.options[i + 1], select.options[i]); } } ()); &lt;/script&gt; </code></pre> <p>However, the Up/Down button takes literally 3-8 seconds to take effect in IE7/8. The first click will sometimes be fast but after that it takes a very long time for the select list to update with the new positions (especially if you have a couple items selected).</p> <p>This problem is not present in Chrome/FF. I wouldn't have thought this simple reordering would be so intensive!</p> <p>Does anyone have any information that could be used to help me speed the moveUp/moveDown functions?!</p>
 

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