In order for you to be able to use markup within a Javascript file, you must either:
1) Modify your .htaccess file to include *.js as a valid extension for files to be processed through the PHP Engine. (Google around for this)
2) Change the Javascript file extension from *.js to *.php.
3) Declare variables which are set through PHP within the main PHP/HTML file, rather than the external Javascript file.
