updux/docs/concepts.md

# Updux concepts

## actions

Updux internally uses the package `ts-action` to create action creator
functions. Even if you don't use typescript, I recommend that you use it,
as it does what it does very well. But if you don't want to, no big deal.
Updux will recognize a function as an action creator if it has a `type`
property. So a homegrown creator could be as simple as:

```js
function action(type) {
    return Object.assign( payload => ({type, payload}), { type } )
}
```


## effects

Updux effects are a superset of redux middleware. I kept that format, and the
use of `next` mostly because I wanted to give myself a way to alter 
actions before they hit the reducer, something that `redux-saga` and 
`rematch` don't allow.

An effect has the signature

```js
const effect = ({ getState, dispatch, getRootState, selectors}) 
                => next => action => { ... }
```

The first argument is like the usual redux middlewareApi, except
for the availability of selectors and of the root updux's state. 

Also, the function `dispatch` is augmented to be able to be called 
with the allowed actions as props. For example, assuming that the action
`complete_todo` has been declared somewhere, then it's possible to do:

```js
updux.addEffect( 'todo_bankrupcy',
    ({ getState, dispatch }) => next => action => {
        getState.forEach( todo => dispatch.complete_todo( todo.id ) );
    }
)
```