How to pass parameters from html.erb to a different html.erb - ruby-on-rails

Question

I'm playing with the messenger gem in rails 4.
I have a graph of nodes and I want to be able to bring up a message box (initially in a different page but will make it a partial later) when a node is pressed so that the current user can message that node.
The id for the clicked node is kept in a div called NameID
At the moment all I've got working is a button that opens the new message page and then you can choose a user from a drop down list. I guess I want that drop down list- the recipient- to be prepopulated from the currently clicked node on the index page.
Here is what I have so far:
index.html.erb
<p><a class="btn btn-lg btn-primary" id="BtnMessageNode" href="/messages/new">Start conversation</a></p>
<div id=NameID><<THIS IS POPULATED BY JAVASCRIPT>></div>
messages_controller.rb
class MessagesController < ApplicationController
before_action :authenticate_user!
def new
#chosen_recipient = User.find_by(id: params[:to].to_i) if params[:to]
end
def create
recipients = User.where(id: params['recipients'])
conversation = current_user.send_message(recipients, params[:message][:body], params[:message][:subject]).conversation
flash[:success] = "Message has been sent!"
redirect_to conversation_path(conversation)
end
end
helpers/messages_helper.rb
module MessagesHelper
def recipients_options(chosen_recipient = nil)
s = ''
User.all.each do |user|
s << "<option value='#{user.id}' data-img-src='#{gravatar_image_url(user.email, size: 50)}' #{'selected' if user == chosen_recipient}>#{user.name}</option>"
end
s.html_safe
end
end
messages/new.html.erb
<% page_header "Start Conversation" %>
<%= form_tag messages_path, method: :post do %>
<div class="form-group">
<%= label_tag 'message[subject]', 'Subject' %>
<%= text_field_tag 'message[subject]', nil, class: 'form-control', required: true %>
</div>
<div class="form-group">
<%= label_tag 'message[body]', 'Message' %>
<%= text_area_tag 'message[body]', nil, cols: 3, class: 'form-control', required: true %>
</div>
<div class="form-group">
<%= label_tag 'recipients', 'Choose recipients' %>
<%= select_tag 'recipients', recipients_options(#chosen_recipient), multiple: true, class: 'form-control chosen-it' %>
</div>
<%= submit_tag 'Send', class: 'btn btn-primary' %>
<% end %>

Answer 1

There are basically two ways to pass parameters to GET routes:
A. Named segments
/users/:user_id/message/new
This nested route would be great if you are sending a message to a single user.
B. Query parameters
Rails supports query parameters as well:
/message/new?to=2
Rails automatically adds query parameters to the params hash. So in this case you would do params[:to].
You can use the Rails route helpers so that you don't have to deal with encoding urls yourself:
new_message_path(to: #user.id)
Use query params for optional parameters like filters and sorting or in this case a preset. Don't use them like users?id=5.