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.

req.get('host') is now deprecated, using it will give Undefined.

Use,

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