Problem with Save As Dialog using Javascript

Hello,

I am facing a Big problem with SaveAs Dialog box created using JavaScript.
My requirement is to allow user to enter the File Name in SAve As Dialog Box in which he/she can save the Data.
I am using "document.execCommand('SaveAs','false','ProfileNam eToSave.xml');" to do this.
But how can I get the path of File Name from execCommand, entered by user into a variable which can be used further to write the Data.
Also I am able to see only the File types as HTML and txt in Dialog.

No help is available on web on this topic. I am stuck badly with this issue.

Thanks is advance.
Regards,