我的ajax调用怎么了？

Im trying to create an ajax call through the following code

$.ajax({
        url: '/',
        method: 'GET',
        data: data
    }).done(function(response){
        console.log(response);
    }).fail(function(){
        console.log("doesn't work");
    })

Controller:

if request.xhr?
  return "hello"
end

The ajax call works but the response I get is a html page and not the actual string "hello". Why is that?

The return value of an controller action is always ignored by Rails. To respond something to the client (browser), you have to use render or one of its derivatives (head, redirect_to, send_file, send_data).

if request.xhr?
  render plain: "hello"
end