Rails默认使用“ text / javascript”内容类型，以响应使用form_for构建的简洁的JavaScript表单

Question

I'm using Rails 4.1.1 and Ruby 2.1.2p95. I am using Slim as my HTML templating language (similar to HAML). I'm using Thin as my Rack server.

I am trying to make a fully-AJAX application (one of my requirements is that I may not reload the page).

PROBLEM

I have a user sign-up page that looks like this:

= form_for( User.new, url: user_path, remote: true ) do |f|
  = f.label :username
  = f.text_field :username, label: true
  = f.label :password
  = f.password_field :password, label: true
  = f.label :password_confirmation
  = f.password_field :password_confirmation, label: true
  = f.submit

I have a UsersController action that looks like this (for the purposes of this example):

  def create
    render html: "PRETEND A USER WAS CREATED"
  end

I have a response handler that looks like this (this is not important really - suffice to say the success handler does not fire and the error handler does):

   $("#dynamic_body").on( "ajax:success", "[data-remote]", function( event, data, status, xhr ) {
      $("#dynamic_body").empty();
      $("#dynamic_body").append( data );
   });
   $("#dynamic_body").on( "ajax:error", "[data-remote]", function( event, xhr, status, error ) {
      $("#dynamic_body").empty();
      $("#dynamic_body").append( error );
   });

Rails sends back a response with a Content-Type header set to "text/javascript". Therefore the browser tries to parse the response as JavaScript, which of course fails, and causes the error event instead of the success event for the AJAX response.

SOLUTIONS THAT I DON'T LIKE

I can fix this by being explicit with Rails, either by specifying the request URL format in the form_for call:

= form_for( User.new, url: user_path( format: :html ), remote: true ) do |f|
  ...

or by specifying the header explicitly in the controller action:

def create
    render html: "PRETEND A USER WAS CREATED", content_type: :html
end

but I'm pretty upset that I even have to do this. Nobody asked Rails to return a javascript response. Their own documentation says that the controller defaults to "text/html" , which is obviously true most of the time but not when using their unobtrusive javascript tools.

I would love to understand what is going on here and if there are any ways I can configure my application so I don't need to write these extra workarounds.

Thanks in advance good people.

Answer 1

Okay I should have guessed this was partly a caching issue when I realized it was inexplicably intermittent. Basically, the solution is simply to force Rails to treat the request as an HTML request, but if the browser has cached the responses as JavaScript before you figure this out, it won't work until you clear the browser cache.

I added the following code to my ApplicationController:

class ApplicationController < ActionController::Base
  ...

  # These two filters together should ensure we return HTML responses to the browser's AJAX reqeusts.
  before_filter :prevent_caching
  before_filter :default_request_format_html

  ...

  private

  ...

  def prevent_caching
    expires_now
  end

  def default_request_format_html
    request.format = "html"
  end
end

These are the minimal forms, which can be made smarter for your needs (eg forcing the request format conditionally). The default_request_format_html callback is the more critical one - if you have this correct from the beginning you theoretically shouldn't need the cache-busting callback.