aurelia-cycle

aurelia-cycle

An Aurelia plugin that allows you to manage Aurelia's View-Bindings functionally, converting them into RxJS observables, consumable as Cycle.js drivers.

Why?

Cycle.js' architecture is arguably better (and definitely more flexible) than the traditional MVC, or even the more recent Flux or Redux programming patterns. It's functional style can be a little overwhelming at first, but thanks to sites like http://rxmarbles.com its concepts are much easier to grasp.

If you're new to Observables or Cycle.js, I'd recommend watching the fantastic talk by Cycle.js' creator, André Staltz:

• What if the user was a function? - Presentation at JSConf BP2015

Why not simply use Cycle.js and forget about Aurelia?

Cycle.js is more of an architecture style, a paradigm, a design concept, than a full-blown web-framework like Aurelia, Angular2 or even React. It's a way of dealing with data coming in and out, in a cycle, and it needs to drive a set of drivers to be useful.

This is one such driver that enables it to drive Aurelia's View-Bindings. Cycle.js has it's own effort to drive the DOM with the use of its DOM Driver, however it is still in an earlier development phase than Aurelia and many issues have yet to be worked out. Aurelia on the other hand is already awesome at driving the DOM, so my thinking was - why not have the best of both worlds?

This way, Aurelia acts as an abstraction layer for the DOM, and all you need to worry about is the pure data that goes in and out.

The added benefit of Aurelia's binding system is that you don't have to go all-pure-and-functional at once - you can mix-and-match, driving only some components using aurelia-cycle, while leaving others to be dealt with by Aurelia.

How to install this plugin?

1. In your project install the plugin and rxjs via jspm with following command

jspm install aurelia-cycle rxjs

1. Make Aurelia load the plugin by adding the following line to the configure function in the main.js file of your src folder

  export function configure(aurelia) {
    aurelia.use
      .standardConfiguration()
      .developmentLogging();

+   aurelia.use.plugin('aurelia-cycle');

    aurelia.start().then(a => a.setRoot());
  }

1. If you use TypeScript or use Visual Studio Code the type declarations for aurelia-cycle should be visible automatically. However you will need to install rxjs to npm to get intellisense for Rx and Observables:

npm install rxjs --save-dev

Using the plugin

The plugin enables you to use Aurelia's View-Bindings as Cycle.js drivers.

To make bindings visible to the driver you need to apply the cycle Binding Behavior to them as shown below:

<template>
  <h2>${count & cycle}</h2>
  <button click.delegate="increment() & cycle">+</button>
  <button click.delegate="decrement() & cycle">-</button>
</template>

This will make Aurelia bypass the default View <-> ViewModel binding and feed the data in and out of the Rx Observables available as sources in the cycle(sources) method.

By defining the cycle(sources) method on a given ViewModel, the plugin will use it to run Cycle.js on it.

By default, one driver is created for you with the name YourClassNameView, but you may manually define the drivers by adding a cycleDrivers property to your ViewModel.

import {Observable} from 'rxjs/Rx'
import {makeAureliaDriver, ViewSource} from 'aurelia-cycle'

export class Counter {
  // commented out, as this is done automatically by default:
  // cycleDrivers = { CounterView: makeAureliaDriver(this) }
  
  cycle({ CounterView }) {
    const action$ = Observable.merge(
      CounterView.actions('increment').map(ev => 1),
      CounterView.actions('decrement').map(ev => -1)
    )

    const count$ = action$
      .startWith(0)
      .scan((total, change) => total + change)

    const sinks = {
      CounterView: count$.map((count) => ({ 
        count: count
      }))
    }
    
    return sinks
  }
}

A ViewSource (CounterView in the above example) exposes two methods (similarly to Cycle.js DOM driver's select(...) and events(...)):

values(bindingName): returns an Observable with all the changes made to the value of the selected two-way binding actions(functionName): returns an Observable of all the calls made to the function of the selected name

The values of the Observable returned by actions(functionName) is an object that contains two properties:

{
  event, // this is the Event that caused the function to be invoked
  arguments // an Array of arguments passed to the function from the View
}

The ViewSink (in the return value of cycle()) should be an Observable of an object, which properties match the bindings names of the View.

The cycle(sources) method is run immediately after bind().

For more examples, see the example repository.

Caveats

Since this is still an early alpha, there are two things that need to be dealt with before this should be used in production:

• Performance: There is no diffing algorithm for complex objects or arrays returned into the sinks, which feed the view engine. This means that if you use a repeat strategy for displaying your data, their Views might get recreated every time new data is fed into the sink.
• Size: This driver uses Observables from RxJS 5, however the Cycle.js is still being rewritten into RxJS 5, and requires Rx 4 as well. Since both libraries have to be loaded, both the size and the initial loading time goes up by quite a bit.

Dependencies

• aurelia-templating
• aurelia-logging
• @cycle/core
• @cycle/rxjs-adapter
• rxjs

Used By

This library isn't used by Aurelia. It is an optional plugin.

Platform Support

This library can be used in the browser as well as on the server.

Building The Code

To build the code, follow these steps.

1. Ensure that NodeJS is installed. This provides the platform on which the build tooling runs.
2. From the project folder, execute the following command:

npm install

1. Ensure that Gulp is installed. If you need to install it, use the following command:

npm install -g gulp

1. To build the code, you can now run:

gulp build

1. You will find the compiled code in the dist folder, available in three module formats: AMD, CommonJS and ES6.

2. See gulpfile.js for other tasks related to generating the docs and linting.

Running The Tests

To run the unit tests, first ensure that you have followed the steps above in order to install all dependencies and successfully build the library. Once you have done that, proceed with these additional steps:

1. Ensure that the Karma CLI is installed. If you need to install it, use the following command:

npm install -g karma-cli

1. Ensure that jspm is installed. If you need to install it, use the following commnand:

npm install -g jspm

1. Install the client-side dependencies with jspm:

jspm install

1. You can now run the tests with this command:

karma start