打字稿和jQuery Ajax

I have the following function:

Updated: added return to $.ajax

searchAjax({url = 'app/php/check.php', data}: {url: any, data: any}): any 
{   
    return $.ajax({
        url: url,
        type: 'post',
        dataType: 'text', 
        data: { data },
        success: function (return_data)
        {   
            return String(return_data);
        },  
        error: function (xhr, status, error) 
        {   
            var err = eval("(" + xhr.responseText + ")");
            console.log(err.Message);
            return err.Message;
        }   
    }); 
}

For now, check.php returns echo 'hi'. Just for testing, I'm trying to console.log the response (in this case return_data). However I get the error EXCEPTION: hi is not defined when I try to console.log it.

Update: Now I get an object with a bunch of stuff and responseText which contains the actual response.