schedule function return until ajax is done

Question

Example of producing!
This is the code used in ajax! I want to schedule the returning of g_text until the ajax is done.

g_text = '@' + text;
    $.ajax({
        url: '/pages/profile/actions.php?action=isusername',
        method: 'POST',
        data: {
            uname: text,
        }
    }).done(function(result) {
        if (result == "true") {
            g_text = '<a target="_blank" href="/?page=profile&base=' + text + '">' + '@' + text + '</a>';
        }
    });
    return g_text;