wordpress use get_canonical_url to help a domain transition when both domains are active (SEO)

functions.php

/* Use get_canonical_url to help a domain transition when both domains are active (SEO) and avoiding penality
 * apply this on old domain and specify new domain
 * Jeff Laflamme <jeff@geekho.asia>
*/
   
add_filter( 'get_canonical_url', 'geekho_get_canonical_url' );
function geekho_get_canonical_url( $canonical_url ) {
        return preg_replace('/oldsite\.com/','newsite.com', $canonical_url);
}