How to pass parameter to js.erb in Rails?

Question

I want to an ajax request to call user controller's xyz action with the passed parameter stage and then append it on #the_box so that I can perform conditional operation like for stage x append @user.age, for stage y append @user.age+1 and for stage z append @user.age-1. How should I do?

I have a html.erb file contains such code:

<center>
  <%= link_to "A", xyz_user_path, stage: "x", remote: true %>
  <%= link_to "B", xyz_user_path, stage: "y", remote: true %>
  <%= link_to "C", xyz_user_path, stage: "z", remote: true %>
</center>
<div id="the_box"></div>

and users_controller.rb has

before_action :set_user, only: [ :xyz]

def xyz
    respond_to do |format|
        format.js {}
    end
end

private
def set_user
    @user = User.find(params[:id])
end

and this xyz.js.erb is what I have now but cannot deal with parameter so it cannot handle conditional operation

$("#the_box").append("<%= @user.age%>");

Answer 1

Here I'm going to access an instance variable defined in wish_me action.

controllers/jserb_controller.rb code:

class JserbController < ApplicationController
  def index
  end
  def wish_me
    @test = 'Hi how are you?'
    respond_to do |format|
      format.js
    end
  end
end

/views/jserb/index.html.erb code:

<div class="wish-me"></div>
<%= link_to "Wish Me", wishme_path, remote: true %>

/views/jserb/wish_me.js.erb

$(".wish-me").append("<%=j @test %>");

config/routes.rb code:

match '/index' => 'jserb#index'
match '/wishme' => 'jserb#wish_me', :as => :wishme

Now try to hit http://<domain-name>/index and then click on WishMe link. So now you are able to pass instance variable to js.erb and accessed the same.

Answer 2

The other answers will help you on here - let me explain them

---

format.js

When you use format.js to filter the mime types, opening brackets basically tells Rails that you want to perform some custom functionality (and hence it won't load the [action].js.erb as default)

If you want to just invoke [action].js.erb, you'll have to call the following:

respond_to do |format|
   format.js #-> will just call [action].js.erb
end

You'll want to read up more about Rails mime types (how to determine XHR requests) & the respond_to block

---

@instance_variables

Secondly, you need to consider the role of @instance variables in your application, and consequently, the method in question.

The main issue you have is you're calling @user in a method which doesn't define it - hence you'll likely see the error undefined method ___ for nil:NilClass or similar

You must remember that Rails is just a gem - a series of classes which runs on the Ruby language. This means that each time you wish to perform a method on an "object" / piece of data, you'll have you to declare / create the object in your Rails application:

def xyz
   @user = User.find params[:id] #-> sets the variable for the duration of the "instance"
   ...
end

Please take note of the name of the variable -- an instance variable. By setting @user (instance variables are always defined with an @), you basically give Rails the ability to access the data inside it for as long as the class which defines the variable is invoked.

Basically means that if you set @user = User.find, it will be available through your view & other helper methods called from the instance of the class

---

Fix

Finally, to address your question directly:

I want to an ajax request to call user controller's xyz action with the passed parameter stage and then append it on #the_box so that I can perform conditional operation like for stage x append @user.age, for stage y append @user.age+1 and for stage z append @user.age-1. How should I do?

#config/routes.rb
resources :users do
   get "xyz/:stage" #-> domain.com/users/:user_id/xyz/:stage
end

#app/views/users/your_view.html.erb
<% links = [["A", "x"], ["B", "y"], ["C", "z"]] %>
<% links.each do |link, stage| %>
    <%= link_to link, xyz_user_path(user, stage: stage), remote: true %>
<% end %>

#app/controllers/users_controller.rb
Class UsersController < ApplicationController
   def xyz
      case params[:stage]
        when "x"
          @user.increment!(:age)
        when "y"
          @user.decrement!(:age)
      end
      respond_to do |format|
         format.js
      end
   end
end

#app/views/users/xyz.js.erb
$("#the_box").append("<%=j @user.age %>");

Answer 3

You should pass the parameter in the helper like this:

xyz_user_path(stage: "x")

And then in your js.erb you can access it like:

<%= params['stage'] %>