Monday, February 13, 2012

Javascript not running in IE8

I encountered a really weird scenario today involving Internet Explorer 8 and javascript. On one particular users computer the browser would not execute any javascript. Even after making sure that javascript was enabled by every other means, the javascript just would not run.

While instpecting all the different IE settings I could find that I thought could influence script execution, I did notice that McAfee had installed scriptproxy as a browser extension. I assumed that this was the most likely culprit causing the unusual application behaviour. I tried disabling the extension, but of course it did not change the situation. 

The reason is that the scriptproxy works by tricking other COM based applications into thinking that it is the jscript or vbscript engine. It does this by changing the registry entries of the jscript and vbscript components so that they actually point back at scriptproxy. So even though I disabled the browser extension, the browser would still be trying to instanciate an instance of scriptproxy and not the jscript component.

Thankfully the system already had Microsoft anti-virus installed and I was given the go-ahead to remove the McAfee component from the computer. 

Unfortunately the McAfee uninstall does not put things back exactly where they were and I was forced to re-register the jscript component manually
regsvr32 jscript.dll
did the trick.

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