Provide Javascript helper object

Hi,

I found myself wanting to inject some Javascript code as the value for the 'initialDate' object but it would get quoted if it goes in as a string so I've added a helper object to get around it.

Details in the doc-string. If you feel it is useful, I'd be happy to try to update the README as well (which I now realised I've forgotten to do!)

Cheers,
Michael