Including JS code that uses PHP

I have some javascript code that has PHP in it like this: var CLIENT_ID='<?php echo $CLIENT_ID; ?>' If I put the JS code directly in a php file with: <script type="text/javascript"> . . . </script> Then at run time CLIENT_ID has the value I want. I want to use the same JS code in many php files. But if I include the JS code like this: <script src="login.js" type="text/javascript"> Then that php code does not get run and CLIENT_ID has the literal string '<?php echo $CLIENT_ID; ?>' Is there a way I can reuse my JS file and still have embedded PHP in it?