RailsでjQueryを読み込まずにmethod: :deleteのリンクを実現する（Routing Error No route matches [GET] ... の対処法） ref: https://qiita.com/y-temp4/items/2d50feb3ff0d65acdf67

devise.rbでdeleteをgetにする

# Use this hook to configure devise mailer, warden hooks and so forth.
# Many of these configuration options can be set straight in your model.
Devise.setup do |config|
  ...
  # The default HTTP method used to sign out a resource. Default is :delete.
  config.sign_out_via = :delete # ここをgetにする
  ...
end

file0.erb

<%= link_to 'ログアウト', destroy_user_session_path, method: :delete %>

file3.erb

<%= button_to 'ログアウト', destroy_user_session_path, method: :delete %>

file5.js

window.onload = () => {

  class Confirm {
    constructor(el) {
      this.message = el.getAttribute('data-confirm')
      if (this.message) {
        el.form.addEventListener('submit', this.confirm.bind(this))
      } else {
        console && console.warn('No value specified in `data-confirm`', el)
      }
    }

    confirm(e) {
      if (!window.confirm(this.message)) {
        e.preventDefault();
      }
    }
  }

  Array.from(document.querySelectorAll('[data-confirm]')).forEach((el) => {
    new Confirm(el)
  })

}

file6.erb

<%= button_to 'ログアウト', destroy_user_session_path, method: :delete, data: { confirm: 'ログアウトしてもよろしいですか？' } %>

HTML出力結果

<form class="button_to" method="post" action="/users/sign_out">
  <input type="hidden" name="_method" value="delete">
  <input type="submit" value="ログアウト">
  <input type="hidden" name="authenticity_token" value="（省略）">
</form>

rails.js

    // Handles "data-method" on links such as:
    // <a href="/users/5" data-method="delete" rel="nofollow" data-confirm="Are you sure?">Delete</a>
    handleMethod: function(link) {
      var href = rails.href(link),
        method = link.data('method'),
        target = link.attr('target'),
        csrfToken = rails.csrfToken(),
        csrfParam = rails.csrfParam(),
        form = $('<form method="post" action="' + href + '"></form>'),
        metadataInput = '<input name="_method" value="' + method + '" type="hidden" />';

      if (csrfParam !== undefined && csrfToken !== undefined && !rails.isCrossDomain(href)) {
        metadataInput += '<input name="' + csrfParam + '" value="' + csrfToken + '" type="hidden" />';
      }

      if (target) { form.attr('target', target); }

      form.hide().append(metadataInput).appendTo('body');
      form.submit();
    },