How to use variable in javascript escape_javascript rails

Question

I found two other posts was the same subject in stackoverflow: How to use variable in javascript escape_javascript rails? and How to use variable in javascript escape_javascript rails?

I applied the solutions exposed, and not only did not work, but something weird happened. Well, at least I think it is weird that's a Ruby variable outputs one result when inspected and a totally different result when printed.

I am developing a rails 6 application where The contents of the Files are as follows:

something.html.erb

<%= form_with(url: "/graficos/partido", method: "get") do |f| %>
    <%= f.button "ClickMe",
           :class => "btn btn-secondary text-white mr-1 active",
           :value => "Clicked",
           :data  => {
                 disable_with: '<i class="fa fa-spinner fa-spin"></i>'.html_safe
            }
          %>
  <% end %>

  <article class="col-9">
    <div id="resultquery">
    </div>
  </article>

something.js.erb

var x=[1,2,3]
x=JSON.stringify(x)
var yt = 99

  $("#resultquery").html("<%= j (render :partial => ‘something’,
                                        :locals => {:xt => '_xt_',
                                                    :yt => " + yt + "
                                                    }
                                ).html_safe
                          %>".replace("_xt_", x ));

_something.html.erb

<p><%= xt.inspect    %></p>
<p><%= xt.class    %></p>
<p><%= xt   %></p>
<p><%= yt   %></p>

And now comes the weird part. The output on the screen shows the following

"[1,2,3]"
String
_xt_
+ yt +

==================================================================

In this example, the approach " … :yt => " + yt + ", … “ Generates the result "+ yt +" (the string itself instead of the value of yt) . Jorawar Singh suggested “=+ yt +-”, Even though I don't understand what this means, it didn't worked to.

The placeholder approach (.replace("xt", x )) generates the weird result:

<p><%= xt.inspect    %></p> gives "[1,2,3]", the value I expected to get
<p><%= xt   %></p>          gives _xt_ (xt[0] => “_”, xt[1] => “x”, ...), the string to be replaced in the  something.js.erb file.

My questions are (q1) How can I pass a parameter since the other approaches didn't work. I did something wrong? (q2) What happened in the placeholder approach? I tried it without stringify and the first result was "1,2,3", and the weird second output was the same.

user1644367 · Accepted Answer · 2020-05-23 17:57:17Z

After lots of research, I was able to find out why the presented approaches do not work. The problem is a misconception about the client-server model.

When the server finds escape to Ruby (<%= ... %>), it replaces the contents with something. In other words: the client do not receive whatever is inside the Escape to Ruby. With this in mind it's easy to see that the first approach ( <%= … :yt => " + yt + " … %>) is doomed: the contents inside the Escape to Ruby will be replaced by the server and so will never arrive the client in this format. In this particular case the server will concatenate all the strings generating something like “... :yt => + yt + …” that will be sent to the client.

The second approach is feasible since the server generates and sends to the client a string containing something like “... :xt => 'xt' … ”. The client into in it's turn to work replaces the xt by whatever it wants to be the value of the parameter. The problem is that it behaves like Schrodinger’s cat: It's value becaames both 'xt' and "[1,2,3]". This must be some Ruby internals, and I have no clue why happens.

Anyway, since both methods do not work I engineered a solution by using actions in a controller that was created just to keep the values of the parameters. In the JavaScript portion of the code, I send an Ajax request to set the value of the parameters in a controller#action class variables. Inside The View I get the controller#action class variable values with a Json request.

Ugly(?), but works.

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