framework/ember/app/views/signup.js

import Ember from 'ember';

import ModalView from 'flarum/mixins/modal-view';

export default Ember.View.extend(ModalView, {
  classNames: ['modal-dialog', 'modal-sm', 'modal-signup'],
  templateName: 'signup',

  didInsertElement: function() {
  },

  welcomeUserDidChange: Ember.observer('welcomeUser', function() {
    if (this.get('welcomeUser')) {
      Ember.run.scheduleOnce('afterRender', this, function() {
        this.$('.signup-welcome').addClass('in');
      });
    }
  })
});