[javascript] How do I get the domain originating the request in express.js?

I'm using express.js and i need to know the domain which is originating the call. This is the simple code

app.get(
    '/verify_license_key.json',
    function( req, res ) {
        // do something

How do i get the domain from the req or the res object? I mean i need to know if the api was called by somesite.com or someothersite.com. I tried doing a console.dir of both req and res but i got no idea from there, also read the documentation but it gave me no help.

Instead of:

var host = req.get('host');
var origin = req.get('origin');

you can also use:

var host = req.headers.host;
var origin = req.headers.origin;

Recently faced a problem with fetching 'Origin' request header, then I found this question. But pretty confused with the results, req.get('host') is deprecated, that's why giving Undefined. Use,

    req.header('Origin');
    req.header('Host');
    // this method can be used to access other request headers like, 'Referer', 'User-Agent' etc.

In Express 4.x you can use req.hostname, which returns the domain name, without port. i.e.:

// Host: "example.com:3000"
req.hostname
// => "example.com"

See: http://expressjs.com/en/4x/api.html#req.hostname