copy_html_controller.js

import { Controller } from "stimulus";

export default class extends Controller {
  static targets = ["source"];

  copy() {
    const range = document.createRange();

    window.getSelection().removeAllRanges();

    this.sourceTarget.classList.remove("hidden");
    range.selectNode(this.sourceTarget);
    window.getSelection().addRange(range);

    document.execCommand("copy");

    this.sourceTarget.classList.add("hidden");
    window.getSelection().removeAllRanges();
  }
}

show.html.haml

%div(data-controller="copy-html")
  %button.btn-teal(data-action="copy-html#copy")
    Copy
  .hidden(data-copy-html-target="source")
    %div(style="background: white; font-size: 11pt; font-family: Calibri; color: black;")
      %br
      %b(style="border: none;") Recent Changes
      %br
      %table(style="width: 800px")
        %thead
          %tr(style="font-weight: bold; color: white; background: #9F5B94; text-align: center;")
            %td(style="border: 1.5pt solid black;")
              Author
            %td(style="border: 1.5pt solid black;")
              Comments
        %tbody
          - @changes.each do |change|
            %tr(style="background: white;")
              %td(style="width: 200px; border: 1.5pt solid black; padding: 2px 10px")
                = change.author.display_name
              %td(style="border: 1.5pt solid black; padding: 2px 10px")
                %ul
                  - change.comments.each do |c|
                    %li(style="border: none; margin: 0;")= c
      %br