WordPress get user id by login name

Solution:1

get_userdatabylogin is now deprecated, it is possible to get the same result via

get_user_by

example :

$user = get_user_by('login','loginname');
if($user)
{
   echo $user->ID;
}

link to the ticket about this change

Solution:2

get_userdata() function is an alias of get_user_by('ID') function. Use this code:

$username = 'your user name';
$user = get_user_by('login', $username);

It will return WP_User object on success, or false on failure. See Codex.

REST APIhttp://example.com/wp-json/wp/v2/users/<id>