how can I pass variable in Express and node.js

I'm trying to do something with node.js and express . but I face some problem in express passing variable to .js

here is my code , I want to know the IP address in the .js , so I do the following things

like this , I redirected the user to the test.js

app.get('/', function(req, res) {
  app.set('ipAddr' , req.ip);
  res.sendfile(__dirname + '/index.html');
});

and index.html include

 <script src="/hello.js"></script>

so , in the hello.js , I want to know the client IP address.

I try to find out how to do it , but I fail.

can anyone tell me how to do it ? really thanks.