Where to place Javascript used in one page only in Rails 7 with importmap

Question

When using Rails 7 with import maps, where do I put code that should be executed by one view only?

Specifically, I have a view that needs to run some Javascript code on load. My Javascript looks something like this:

import {TheController} from "./TheController"

let controller = new TheController();

document.onreadystatechange = function () {
  if (document.readyState === 'complete') {
    controller.onLoad();
  }
};  

How do I setup the Javascript environment so that the document.onreadystatechange code is executed only by the desired view? (Everything almost works when I put this code in a file imported by application.js, but then it gets executed by every view.)

I suspect the answer is to create separate importmaps and importmap_tags; but, I can find any demonstrations of how to do that in Rails 7.

Answer 1

As @Azrklm points out, the answer is contained in this video https://youtu.be/PtxZvFnL2i0?t=1287 beginning at time 21:38.

Suppose we have some JavaScript that we want to run only on a view called FancyView. Here are the steps

1. Place the code unique to FancyView in its own file, say FancyView.js (and remove it from application.js, if necessary).

2. Add a line for FancyView.js to the importmap: pin "FancyView"

3. Add the line <%= yield :head %> to application.html.erb`. (This tells Rails that individual views/layouts may want to add additional information to the web page's head.)

   <%= stylesheet_link_tag "application", "data-turbo-track": "reload" %>
   <%= javascript_importmap_tags %> <%# This loads application.js %>
   <%= yield :head %>
   

4. Add a javascript_import_module_tag to the view:

   <% content_for :head do %>
     <%= javascript_import_module_tag "FancyView" %>
   <% end %>
   

Answer 2

If anyone has a similar problem finds this question, I found the answer from @Zack to be perfectly concise and exactly what I needed, BUT with 2 important caveats:

1. I couldn't use the capcase naming convention for my js. FancyView needed to be fancyView.

2. The javascript_import_module_tag should come after your javascript_importmap_tags

   <%= javascript_importmap_tags %>
   <%= yield(:head) %>
   

This is also now explained on the rails github page: https://github.com/rails/importmap-rails#selectively-importing-modules

Thanks @Zack!

Answer 3

DHH explains it pretty well have a look plz https://youtu.be/PtxZvFnL2i0?t=1287