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The well-known HTML5 testing library Modernizr 1.5 doesn’t work correctly in the MSIE9 Platform Preview browser. The reason is a non-standard IE9PP behavior, which isn’t sanitized in the library code.

The Modernizr library tests some properties with a such code:

if (m_style[property] !== undefined) ...

m_style is a shortcut for testing element’s style:

m = doc.createElement( mod ),
m_style = m.style

There are five properties tested in a CSS3 transformation test: ‚transformPro­perty‘, ‚WebkitTransform‘, ‚MozTransform‘, ‚OTransform‘ a ‚msTransform‘. The problem occurs in the IE9PP browser, which correctly returns undefined for the four properties, excepting the last one. Accessing the msTransform property doesn’t return either undefined or an object, but throws a „Not Implemented“ exception. test_props() function in the Modernizr library ver. 1.5 doesn’t catch this exception (nobody expects an exception here), so the whole script fails.

We can hope that next version of the IE9 browser (maybe the public beta) will fix it. Paul Irish, the Modernizr contributor, also reported it as a bug.

We can fix the Modernizr 1.5 library by enclosing the test into a try{} block, and catching the exception. Here is a patched version:

function test_props( props, callback ) {
    for ( var i in props ) {
        try {
          if ( m_style[ props[i] ] !== undefined && ( !callback || callback( props[i], m ) ))
             {return true;}
        } catch (e) { ; }
    }
}

We’ve been noticed about the problem, which affect our HTML5 Support Detector, by Štěpán Bechynský.