Your example shows the most simple way of passing PHP variables to JavaScript. You can also use json_encode for more complex things like arrays:
Other than that, if you really want to "interact" between PHP and JavaScript you should use Ajax.
Using cookies for this is a very unsafe and unreliable way, as they are stored clientside and therefore open for any manipulation or won't even get accepted/saved. Don't use them for this type of interaction.
jQuery.ajax is a good start IMHO.
