skyrocket

Seamlessly upgrade Taunus applications to a realtime festivus

Intended for use after you've set up Taunus and gradual along with it.

Motivation

Skyrocket sets you up to do realtime with Taunus without radically changing your application and while staying on the progressive enhancement course. Think of skyrocket as the data-binding aspect of Taunus. Instead of spending most of your time on getting data-binding right, you'll be spending time on getting realtime updates right.

These updates are one-way (model to view). Model-to-view is effective because any impact you have on the view should ultimately persist changes on the server, which should end up triggering a skyrocket back to your client (and other interested parties), which will in turn update the view with those model changes.

Requirements

• Taunus
• WebSockets (we suggest socket.io but you can use anything)

Install

npm install skyrocket --save

Setup

There's a little configuration to be done around skyrocket mostly so that it stays transport and authentication agnostic. I'll explain how you can set up skyrocket naïvely and try to explain along the way where you might want to reinforce your application.

We'll need:

• A server-side WebSocket endpoint to listen for events
• A server-side WebSocket endpoint to stop listening for events
• A client-side WebSocket endpoint to handle any updates

Here's both of the server-side endpoints that let a user join and leave rooms at will. In the real world you should probably verify the user is authorized to join a given room. This is entirely left up to you. You are also completely free when it comes to the endpoints you want to use.

server.on('connection', connected);

function connected (socket) {
  socket.on('/skyrocket/join', join);
  socket.on('/skyrocket/leave', leave);

  function join (data) {
    data.rooms.forEach(socket.join);
  }
  function leave (data) {
    data.rooms.forEach(socket.leave);
  }
}

On the client-side, you'll need to tell skyrocket to use these endpoints to join and leave channels ("rooms" in socket.io terminology). The revolve method gets called with the type of action skyrocket needs to perform (join or leave), and the rooms that need to be entered or abandoned. Keep in mind, it's up to the server to grant or revoke access to any given room.

var client = require('socket.io-client');
var io = client('');
var taunus = require('taunus');
var skyrocket = require('skyrocket');

skyrocket.configure({
  revolve: revolve
});

function revolve (type, rooms) {
  io.emit('/skyrocket/' + type, { rooms: rooms });
}

Lastly, you'll want to set up skyrocket.react handlers whenever a gradual response comes in, and also whenever a realtime payload is received. Again, the /skyrocket/update endpoint could also be changed to some other route of your choosing.

taunus.gradual.on('data', skyrocket.react);
io.on('/skyrocket/update', skyrocket.react);

Usage

Now that the skyrocket is armed, you can send updates from the server-side to all relevant clients. Typically, you'll want to respond on an HTTP request with the payload, and send the same update to all listeners in the room.

Here's a (simplified) example where a card was moved in a Stompflow sprint board. This update doesn't do anything, but we'll get to more meaningful updates, and their schema, in just a bit.

var room = '/stompflow/stompflow/sprints/1/move';
var data = {
  updates: [{
    rooms: [room]
  }]
};
res.json(data);
socket.to(room).emit('/skyrocket/update', data);

Only clients who are actually in that room will get the update, along with the recipient of the JSON response.

We haven't yet gotten to what the update looks like, or how it gets handled on the client-side, but note how we're able to treat responses exactly the same as realtime updates? This means that your data-binding efforts will effectively lay out most of the groundwork for realtime interactions in your Taunus applications.

Skyrocket Schema

Before we get to how you'll handle these "updates", we need to look into how they look like and how they work. Updates get applied against a view model or a portion of a view model. At their most basic, consider the update shown below.

{
  updates: [{
    rooms: ['/stompflow/stompflow'],
    model: {
      description: 'Hazelnuts!',
      foo: {
        bar: 'baz'
      }
    }
  }]
}

This update gets applied against a model using assignment, replacing whatever description value with 'Hazelnuts!'. If model.foo already existed, then only model.foo.bar would be changed to 'baz', and the rest of that tree will stay intact. This makes it easy to update bits of a model without compromising the rest, and without demanding that you send the whole model through the wire every single time a value changes.

Operations

Arrays are a little different because many times we want to remove a specific item, add something to the end of the collection, or maybe even add something to the beginning. Sometimes we just want to edit an item! To get around all of these, skyrocket has the concept of operations.

Suppose you had a view model like this:

{
  thread: {
    comments: [{
      id: 1,
      author: 'bevacqua',
      text: 'this seems pretty verbose'
    }, {
      id: 2,
      author: 'BUYSELLSHOES.COM',
      text: 'SHOES ARE THE BEST. BUY BUY BUY, offers. prada! nike!'
    }]
  }
}

If for some reason you wanted to submit an update indicating that the second comment should be deleted, the following would suffice. Note how the concern property is used to figure out what it is that should be updated, and op indicates we want to remove an element from the collection. Similarly, query indicates what it is we want removed.

{
  updates: [{
    rooms: ['/stompflow/stompflow'],
    operations: [{
      concern: 'thread.comments',
      op: 'remove',
      query: { id: 2 }
    }]
  }]
}

Want to add another comment instead? Just use the push operation, this time we'll have to add the model as well, but we don't need a query. You could also use unshift if you want the element at the beginning of the list instead.

{
  updates: [{
    rooms: ['/stompflow/stompflow'],
    operations: [{
      op: 'push',
      concern: 'thread.comments',
      model: {
        id: 3,
        author: 'hackernewsexpert',
        text: 'Shoes are not that useful. Research shows sandals are better.'
      }
    }]
  }]
}

Lastly, editing a comment is just as easy.

{
  updates: [{
    rooms: ['/stompflow/stompflow'],
    operations: [{
      concern: 'thread.comments',
      op: 'edit',
      query: { id: 3 },
      model: {
        text: 'Shoes are terrible. Big data shows sandals are way better.'
      }
    }]
  }]
}

Whenever the straightforward model updates or the array operations aren't enough, you can resort to a custom applyChanges option in the view controller. How is it that you can actually update a view model using all of this, then?

Consider the case where you have a timeline thread that can be watched for notifications. When the button gets clicked the action changes from Watch to Unwatch, or viceversa. As you can see here, the changes to the viewModel are entirely conducted by skyrocket, and your view controller can focus on re-rendering the relevant portion of the view. Effectively, this is one-way data-binding from your model to your view.

var taunus = require('taunus');
var skyrocket = require('skyrocket');

module.exports = function timelineController (viewModel, container, route) {
  var rocket = skyrocket.scope(container, viewModel);

  rocket.on(route.pathname + '/timeline/watch-unwatch', onchange);

  function onchange () {
    taunus.partial($.findOne('.tl-watch-actions'), 'projects/timeline/watch-unwatch', viewModel);
  }
};

You do have to break up the views in as many small components as you deem necessary, but modularity is hardly a bad thing.

API

The skyrocket API comes with a few distinct methods.

skyrocket.configure(options)

The options that you can pass to this method are:

• revolve(type, rooms), a method that will be invoked whenever Skyrocket needs to join or leave a room via WebSocket
• joining(reactor), a method that will be invoked whenever entering a room on the client-side

The reactor object contains all sorts of relevant pieces.

• container is the DOM element passed to skyrocket.scope when setting up the listening context
• viewModel is the model passed to skyrocket.scope when setting up the listening context
• room is the room this reactor is listening on
• applyChanges is the method with which updates to the viewModel will be applied
• reaction is the method that will get called after changes get applied
• destroy should be invoked whenever the reactor is deemed no longer necessary

skyrocket.op(name, handler)

Add your own custom operations in the client-side. As an example, the operation below will replace the target value with the result of adding operation.value to it.

skyrocket.op('add', function (target, operation) {
  return target + operation.value;
});

So with a model like { foo: 1 }, an operation like { op: 'add', concern: 'foo', value: 2 } will result in a model like { foo: 3 }.

If the operation handler doesn't return a value, the target won't be replaced. Note that replacing a target is only feasible if a concern is provided. You can always use target by reference to change child properties in it. The example below would have a similar effect as long as you specified prop: 'foo' and didn't provide a concern.

skyrocket.op('add-child', function (target, operation) {
  target[operation.prop] += operation.value;
});

skyrocket.scope(container, viewModel)

Typically invoked once per view controller, this method returns a rocket object that's able to listen in on rooms.

rocket.on(room, options?, reaction?)

Whenever room gets an update, applies changes to viewModel and fires reaction(update). The options object may be omitted. Options include:

• applyChanges(viewModel, update) is meant to apply an update to a viewModel. Advanced, shouldn't be necessary in most use cases

skyrocket.react(data)

For the most part this should be wired as explained at the end of the setup section. This method is used to signal an incoming event that should be handled to update any relevant view models and re-render affected parts of a view.

License

MIT