discourse/app/assets/javascripts/discourse/mixins/open-composer.js.es6

// This mixin allows a route to open the composer
import Composer from 'discourse/models/composer';

export default Ember.Mixin.create({

  openComposer(controller) {
    this.controllerFor('composer').open({
      categoryId: controller.get('category.id'),
      action: Composer.CREATE_TOPIC,
      draftKey: controller.get('model.draft_key'),
      draftSequence: controller.get('model.draft_sequence')
    });
  },

  openComposerWithTopicParams(controller, topicTitle, topicBody, topicCategoryId, topicCategory, topicTags) {
    this.controllerFor('composer').open({
      action: Composer.CREATE_TOPIC,
      topicTitle,
      topicBody,
      topicCategoryId,
      topicCategory,
      topicTags,
      draftKey: controller.get('model.draft_key'),
      draftSequence: controller.get('model.draft_sequence')
    });
  },

  openComposerWithMessageParams(usernames, topicTitle, topicBody) {
    this.controllerFor('composer').open({
      action: Composer.PRIVATE_MESSAGE,
      usernames,
      topicTitle,
      topicBody,
      archetypeId: 'private_message',
      draftKey: Composer.NEW_PRIVATE_MESSAGE_KEY
    });
  }

});