Unintentionally Overwriting Stylesheets in IE

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As part of a recent request to customize the header of a SharePoint (MOSS 2007) site, I ran into a little problem when trying to dynamically replace a stylesheet using Javascript.  The page had two stylesheets loading, one core stylesheet and one theme stylesheet, in that order.  I was trying to replace the core stylesheet with an altered version for certain parts of the site, however when I did it was as if the theme stylesheet was being overwritten too.  The problem was in how IE handles the DOM and Stylesheets (this was not a problem in Firefox). 

I started by creating a new stylesheet link element, then replacing the existing one with the new one (see code below).

var newElement = document.createElement("link");
newElement.type = "text/css";
newElement.rel = "stylesheet";
newElement.href = "/_layouts/1033/styles/core_orig.css";
newElement.media = 'screen';

var oHead = document.getElementsByTagName("head")[0];
var aLinks = oHead.getElementsByTagName("link");

for (var li = 0; li < aLinks.length; li++) {
   if (aLinks.href.indexOf("core.css") > -1) {
        oHead.replaceChild(newElement, aLinks[li]);

This was the first instance of seeing the problem with my theme.css being overwritten.  I then tried just doing a simple replace on the link href to replace core.css with core_orig.css.  Again, the same results.  In both cases it seemed as if the replace just wasn't happening at all.  After some exploring using the ever helpful Firebug and the IE Dev Toolbar I realized the replace was happing, it just wasn't behaving as expected. 

So finally I realized it was just a matter of the order of things occuring, as it often is.  In this case, IE was loading core.css, then theme.css then in javascript I was loading core_orig.css which because of similar classes was basically overwritting them both.  In Firefox this wasn't an issue as it just replaced the core.css as I wanted but IE reinterpreted it again after the other two had already loaded.  So now all I had to do was just drop and recreate the theme.css after replace the core.css and I was done (final code below).

var url=window.location.href.toLowerCase();
if (url.indexOf('/sites/') > -1 || url.indexOf('/sitedirectory/') > -1) {
var oHead = document.getElementsByTagName("head")[0];
var aLinks = headID.getElementsByTagName("link");

var newElement = document.createElement('link');
newElement.type = 'text/css';
newElement.rel = 'stylesheet';
newElement.href = '/_layouts/1033/styles/core_orig.css';
newElement.media = 'screen';

for (var ci = 0; ci < aLinks.length; ci++) {
if (aLinks[ci].href.indexOf('core.css') > -1) {
var newHref = aLinks[ci].href;
newHref = newHref.replace("core.css", "core_orig.css");
newElement.href = newHref;
oHead.replaceChild(newElement, aLinks[ci]);
} else if (aLinks[ci].href.indexOf('/_themes/') > -1) {
var newNode = aLinks[ci].cloneNode();
Relevant Tags: SharePoint | Browsers | JavaScript | CSS