Conditional loading of components

gistfile1.txt

# posts/show.html.erb
<%= react_component("ShowPost", render(template: 'posts/show.json.jbuilder')) %>


# posts/show.json.jbuilder
json.post do
  json.extract!(@post, :id, :user_id, :title, :body)
end
json.comments(@comments) do |comment|
  json.extract!(comment, :id, :user_id, :body)
end if @comments
json.users(@users) do |user|
  json.extract!(user, :id, :name)
end if @users


# controllers/posts_controller.rb
def show
  @post = Post.find(params[:id])
  if some condition
    @comments = @post.comments.includes(:user)
    @users = @comment.flat_map(&:user).uniq
  end
end


// components/show_post.js.jsx
var ShowPost = React.createClass({
  propTypes: {
    post:     React.PropTypes.object.isRequired,
    comments: React.PropTypes.array,
    users:    React.PropTypes.array
  },


  render: function() {
    var comments = null;
    if (this.props.comments !== undefined) {
      comments = (
        <div>
          <h2>Comments</h2>
          <CommentsList comments={this.props.comments} usres={this.props.users} />
        </div>
      );
    }

    return (
      <div>
        <h1>{this.props.post.title}</h1>
        <Post post={this.props.post} />
        {comments}
      </div>
    );
  }
});

Ok, now a Flux version (of the JS only).

Yes, there's a lot more files here. But if you're using these stores over multiple components, the initial overhead pays out completely over time. You can also define helpers to make the coding DRYer (we have a BaseStore that all our stores extend from, and it takes care of all the repetitive events setup).

# components/show_post.js.jsx
var ShowPostController = React.createClass({
  propTypes: {
    postId: React.PropTypes.number.isRequired
  },

  getInitialState: function() {
    // Maybe the stores have some data, maybe not. We don't care actually
    // because we're going to listen to them for changes later on.
    return this.getStateFromStores();
  },

  getStateFromStores: function() {
    return {
      posts: PostStore.get(this.props.postId),
      comments: CommentStore.getByPostId(this.props.postId),
      users: UserStore.getAll()
    }
  },

  setStateFromStore: function() {
    this.setState(this.getStateFromStores());
  }

  componentDidMount: function() {
    // Listen to the stores for changes. Any time one or all of them change, the
    // component will be re-rendered.
    PostStore.addChangeListener(this.setStateFromStores);
    CommentStore.addChangeListener(this.setStateFromStores);
    UserStore.addChangeListener(this.setStateFromStores);

    // Ok, now we can ask an Action Creator to grab data from the API and send it
    // through the dispatcher!
    PostActionCreator.fetchPost(this.props.postId);
  },

  componentWillUnmount: function() {
    // Remember to unbind those event so we avoid zombie component errors
    PostStore.removeChangeListener(this.setStateFromStores);
    CommentStore.removeChangeListener(this.setStateFromStores);
    UserStore.removeChangeListener(this.setStateFromStores);
  },

  render: function() {
    // Since the data might not be here yet, we need to define a possible loading state:
    if (!this.state.posts) {
      return <div><em>Loading the post! Be right with you...</em></div>;
    }

    // The rest is the same as your example except this.props.whatever is replaced
    // with this.state.whatever
    var comments = null;
    if (this.state.comments !== undefined) {
      comments = (
        <h2>Comments</h2>
        <CommentsList comments={this.state.comments} users={this.state.users} />
      );
    }

    return (
      <div>
        <h1>{this.state.post.title}</h1>
        <Post post={this.state.post} />
        {comments}
      </div>
    );
  }
});


# actions/PostActionCreator.js
PostActionCreator = {
  fetchPost: function(postId) {
    // Choose your own ajax:
    ajax({
      url: '/posts/show/'+this.props.postId+'.json',
      success: function(postData) {
        // Cool, we got the data! Now what? Well, we send it through the Dispatcher
        // so that any stores that want can grab the data and use it!

        // This data payload is the actual "action" in Flux terminology.
        var action = {
          type: 'GET_POST_SUCCESS',
          data: postData
        };

        Dispatcher.dispatch(action);
      }
    });
  }
}


# dispatcher: https://github.com/facebook/flux/blob/master/src/Dispatcher.js
# Won't detail this here, but basically it's a hub for all actions to flow through
# the system. The stores below will register listeners to the dispatcher, and every
# single dispatched action will be processed by them. This is the central part of
# the Flux "one-way data flow" — no data should _ever_ enter the system except through 
# the dispatcher.


# stores/PostStore.js
// Keep a PRIVATE stash for the data. Stores should only have public GET methods,
// and no SET methods. The only way to modify data in a store is to dispatch an
// action that the store listens for.
var _posts = {};

// Extend functionality from EventEmitter. This lets the store emit change events,
// like the ones the Component is listening for.
var PostStore = merge(EventEmitter.prototype, {

  // First three functions are all EventEmitter-related
  emitChange: function() {
    this.emit('CHANGE');
  },

  addChangeListener: function(callback) {
    this.on('CHANGE', callback);
  },

  removeChangeListener: function(callback) {
    this.removeListener('CHANGE', callback);
  },

  // Public getter so components can access the data
  get: function(postId) {
    return _posts[postId];
  }
});

// Listen to every action that goes through the Dispatcher. Only do stuff with the
// actions you care about.
Dispatcher.register(function(action) {
  if (action.type === 'GET_POST_SUCCESS') {
    // Cool! We know that this action has some data for us! So let's set it:
    this._posts[action.data.post.id] = action.data.post;

    // And now, any components that rely on us might want to know that something's
    // changed, so they can re-render. Let's run our emitChange event, and anyone
    // who's addChangeListener'd us will have their callback fired:
    PostStore.emitChange();
  }
});


# The other stores are similar, but they define their own get methods. For example,
# a truncated CommentStore might look like this:

var _comments = {};

var CommentStore = merge(EventEmitter.prototype, {
  // event stuff...

  getByPostId: function(postId) {
    var comments = [];

    // Loop through all the private comments object and make an array of all the
    // comments that have the given post_id. This is how we do related data.
    for (id in _comments) {
      if (_comments[id].post_id === postId) {
        comments.push(_comments[id]);
      }
    }
  }
});

Dispatcher.register(function(action) {
  if (action.type === 'GET_POST_SUCCESS') {
    // There _may_ or _may not_ be comments here. Let's check:
    if (this.action.comments) {
      // Yissssssss
      this.action.comments.forEach(function(comment) {
        _comments[comment.id] = comment;
      });
      CommentStore.emitChange();
    }
  }
});