jQuery Ajax请求不会触发来自Rails控制器的JS响应？

我有一个设置为响应HTML，JS和JSON请求的标准控制器：

I have a standard controller which is set up to respond to HTML, JS and JSON requests:

def picture
  @picture = Picture.new params[:picture]

  respond_to do |format|
    if @picture.save
      format.html do
        logger.debug "In the HTML responder"
        redirect_to @picture
      end
      format.json { render json: @picture, status: :created, location: @picture }
      format.js { render :nothing => true }
    else
      # you get the idea
    end
  end
end

现在我正在尝试使用 $。ajax 函数向该控制器发送请求（我不能使用：remote => true （在这种情况下-我正在尝试使ajax文件上传正常）。

Now I'm trying to send a request to that controller with the $.ajax function (I can't use :remote => true in this specific situation - I'm trying to make ajax file upload work).

$.ajax({
  url: $("form#new_picture").attr("action"),
  type: "POST",
  data: formdata,
  processData: false,
  contentType: false
});

问题是由于某种原因我的请求被视为HTML请求。

The problem is that my request is being treated as a HTML request for some reason. How do I tell rails that I want a JS response?

顺便说一下，我在项目中使用的是jquery_ujs，因此我可以在需要时使用它提供的方法。我对JS的调整还不够好，无法完成我在这里所做的事情。

By the way, I'm using jquery_ujs in my project so I have access to the methods it provides if necessary. I'm not really good enough at JS to tweak that to do what I need here.