Express.js: how to get remote client address

I don’t completely understand how I should get a remote user IP address.

Let’s say I have a simple request route such as:

app.get(/, function (req, res){
   var forwardedIpsStr = req.header('x-forwarded-for');
   var IP = '';

   if (forwardedIpsStr) {
      IP = forwardedIps = forwardedIpsStr.split(',')[0];  
   }
});

Is the above approach correct to get the real user IP address or is there a better way?
And what about proxies?