Effects

[nhunzaker]

This PR adds the concept of effects to Microcosm, a way to apply side-effects in a safe way. Whenever an action moves into a new state, it asks the history object to reconcile. After reconciliation, I've added an extra step for handling side effects. This should support a few use cases:

1. Side-effects in presenters that are the result of actions happening
2. Secondary data fetching

const repo = new Microcosm()

const Notifications = {
  notify (repo, params) {
    alert(params.name + ' was updated!')
  }

  register() {
    return {
      [createUser] : this.notify
    }
  }
}

repo.addEffect(Notifications)

repo.push(createUser, { name: 'Billy' })

These can be added to Presenters too, and localized to a particular fork. So side-effects can be managed more strategically than a simple register method:

class MyPresenter extends Presenter {
    setup (repo) {
        repo.addEffect(Effect, { options })
    }
}

[greypants]

oh, nice. Didn't realize you could do that inline. Sad that we can't make a global exception for this pattern 😞

[nhunzaker]

Ack! This file should get removed. Good catch!

[nhunzaker]

Beyond that though, I want to say there's a thing you can do with no-unused-vars that ignores variables that start with _.

[greypants]

I like it. I need to sit with the term Effect for a bit, but I think this is super helpful. Minor concerns/things to think about: Domains, Presenters, and Effects are all feel super similar in that they all have register methods and callbacks. A newbie might wonder why they can't just use domains for this purpose, since they look the same and work similarly. Maybe just an issue of documentation though.

[coveralls]

Coverage remained the same at 100.0% when pulling 72b7fc8 on effects into d4da2cc on master.

[greypants]

This probably screws up a bunch of naming internals, but I almost think this would be nice:

class MyPresenter extends Presenter {
    setup (repo) {
        repo.register(Effects, { options })
    }
}

Just an idea. Not married to it. Just thinking that repo.addEffect could be clearer or more descriptive. Or not!

[coveralls]

Coverage remained the same at 100.0% when pulling 62a113f on effects into d62f888 on master.

[nhunzaker]

@greypants I hear you on the similarity. There's something there that I haven't figured out yet. I'm okay with it being a little confusing for the sake of consistency, but I agree that the documentation needs to be clearer.

[coveralls]

Coverage remained the same at 100.0% when pulling 16c7388 on effects into 36121a7 on master.