Web site exhibits JavaScript error on iPad / iPhone under 3G but not under WiFi

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I’ve investigated this further and discovered that the problem is that the UK mobile operator O2 (the original exclusive iPhone operator for Apple), modifies web content before sending it to iPhones and iPads. Probably before sending it to any device running a mobile browser.

They non-deterministically inline some of the CSS and JavaScript into the main source files of the web pages. This can create errors either because of mistakes in their algorithm or the consequence of stripping white space from source files with syntactic mistakes in the source files which were otherwise benign.

These modifications also strip copyright messages from copyrighted javascript libraries and css libraries and play havoc with delivery optimisations.

For example, imagine if a user is visiting a sequence of pages on your site which all link to jQuery libraries. Instead of letting your mobile browser locally cache the library, O2 inline the library on every page, forcing your phone to load the entire library over and over again for every page.

I’ve written a blog about the issue here in the hope if drawing a bit more attention to this: http://stuartroebuck.blogspot.com/2010/07/mobile-proxy-cache-content-modification.html

My workaround is to use document.write() to insert the JavaScript library dependencies at load time and prevent O2 from inlining them. This seems to work quite well. e.g.:

<script type="text/javascript">
// <![CDATA[
// Using document.write to load JavaScript dependencies to bypass O2 network inlining of JavaScript.
function loadJS(file){document.write("<" + "script type="text/javascript" src="" + file + ""></" + "script>")}
loadJS("/js/jquery-1.4.2.min.js");
loadJS("/js/myJSLibrary.js");
// ]]>
</script>

Note that, as ever, document.write will not work if the page is served as XHTML.

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