Add class to Ember Application (after 2.7.0)

app-view.js

// instance-initializers/app-view.js
// With an instance initializer, we can register a component for Ember to use at the top level.
// Not ideal, but it works in the meantime until routable components drop.

import Ember from 'ember';

const AppView = Ember.Component.extend({
  classNames: ['my-app'],
});

export function initialize( appInstance ) {
  appInstance.register('view:toplevel', AppView);
}

export default {
  name: 'app-view',
  initialize
};

After some back and forth it seems that this implementation no longer works on 2.10.0-beta.2

If it's only needed to set a class based on the route (that was my use-case) this may do as an alternative:

import Ember from 'ember';

const NAME_SUFFIX = '-route';

export default Ember.Controller.extend({

  _updateRouteClass: function() {
    let routeName = this.get('currentRouteName');

    if (routeName) {
      let name = routeName.dasherize().replace(/\./g, '-') + NAME_SUFFIX;
      let bodyEl = document.querySelector('body');

      Array.from(bodyEl.classList).forEach((klass) => {
        if (klass.endsWith(NAME_SUFFIX)) {
          bodyEl.classList.remove(klass);
        }
      });

      bodyEl.classList.add(name);
    }
  }.observes('currentRouteName').on('init'),

});