res.append()

res.append(field [, value])

Appends the specified value to the HTTP response header field. If the header is not already set, it creates the header with the specified value. The value parameter can be a string or an array.

Note: calling res.set() after res.append() will reset the previously-set header value.

res.append('Link', ['<http://localhost/>', '<http://localhost:3000/>']);
res.append('Set-Cookie', 'foo=bar; Path=/; HttpOnly');
res.append('Warning', '199 Miscellaneous warning');