The issue is probably here:
Code:
window.open(url,'Image','width=largeImage.stylewidth,height=largeImage.style.height,resizable=1');
That third argument is a literal string and yet you have included variable names in there as though they will be automatically replaced with values. That should be:
Code:
window.open(url, 'Image', 'width=' + largeImage.style.width + ',height=' + largeImage.style.height + ',resizable=1');
Note that you were missing a dot too, so it wouldn't have worked even if they were replaced automatically.

Note that JavaScript also supports a feature akin to .NET string interpolation but it's not supported in (at least some versions of) IE so you can't use it if you want that wide browser support.