Managex

Predictable state manager with zero boilerplate, where actions are just functions with built-in support for asynchronous operations and promises. It can be described in the three fundamental principles of Redux but requires less boilerplate while let you to focus in application related concerns.

import {StateManager} from 'managex'

// initialize state manager
const state = {count: 0}
const stateManager = new StateManager(state)

// action
const increment = async (state, x) => state.count + x

// execute actions
stateManager.do(increment, 1).then(state => {
  expect(state.count).toBe(2)
})

The three fundamental principles of Redux

1. Single source of truth
2. State is read-only
3. Changes are made with pure functions

My team needed to quickly adopt a predictable state manager. Since the adoption of Redux requires to deal with Actions, Actions Creators, Reducers, Combined Reducers, Middlewares, and a few more clever-named concepts, most of them comming from functional programming. I thought such adoption would be faster if we introduce a tool that sinthetizes those 3 fundamental principles in something more simple, with boring names, and less boilerplate.

Managex it just about a State Manager and plain functions called Actions .

The state manager

The state manager holds the appliction state. It is the responsible of updating the application state by wrapping the actions execution, and notifying to the listeners after each state update.

const sm = StateManager.from(INITIAL_STATE)
// alternatively
const sm = new StateManager(INITIAL_STATE)

Reacting to state changes

The state can be observed by subscribing a listener to the state manager.

const sm = StateManager.from(INITIAL_STATE)

sm.subscribe((newState) => {
  console.log(newState)
})

The subscribe method returns a function that will unsubscribe the added listener if executed.

const unsubscribe = sm.subscribe((newState) => {
  console.log(newState)
  unsubscribe()
})

Actions

Actions are plain functions that receives the state as the first argument. The rest of arguments are passed trough do and will methods of the state manager.

const INITIAL_STATE = {
  count: 1
}

function add(state, x) {
  return {
    ...state,
    count: state.count + x
  }
}

sm.do(add, 3)

// sm.getState().count == 4

The will method returns a functions that commits the provided action when executed.

const deferredAction = sm.will(add, 3)
deferredAction() // execute

// sm.getState().count == 4

Promises and asynchronous actions

Actions can be asynchronous or return a Promise. The state manager will handle either case updating the state when appropiated.

const INITIAL_STATE = {
  count: 1
}

async function add(state, x) {
  return {
    ...state,
    count: state.count + x
  }
}

sm.do(add, 3).then(() => {
  //sm.getState().count == 4
})

Usage with React

Managex comes with built-in React integration. It has few primitives:

• Provider, is a React component that takes a state manager and injects it to each descendant through React contexts.
• Observers are React components aware of the state manager.

To use Observers you need to implement a special method called mapState that tells how to transform the application state to the React component state. Example:

import {Observer} from 'managex'

class TodoList extends Observer {
  mapState(state) {
    return {
      todos: state.todos
    }
  }

  render() {
    return <ul>{this.state.todos.map(todo => <TodoItem name={todo.name} />)}</ul>
  }
}

The StateManager instance in provided as a property in each observer component. It can be referenced as stateManager.

import {Observer} from 'managex'

class TodoList extends Observer {
  ...

  renderTodos() {
    return this.state.todos.map(todo => (
      <TodoItem
        name={todo.name}
        onClick={() => this.stateManager.do(completeTodo, todo.id)}
      />
    ))
  }

  ...
}

Example integrating Provider and Observer:

import {Component} from 'react'
import {Provider, Observer} from 'managex'

// action
function toggleTodo(state, todoId) {
  return {
    ...state,
    todos: state.todos.map(todo => {
      if (todo.id === todoId) todo.completed = !todo.completed
      return todo
    })
  }
}

// component
class TodoItem extends Component {
  render(props) {
    return (
      <li>
        {props.name}
        <button onClick={props.onToggle}></button>
      </li>
    )
  }
}

// observer
class TodoList extends Observer {
  mapState(state) {
    return {
      todos: state.todos
    }
  }

  renderTodos() {
    const sm = this.stateManager

    return this.state.todos.map(todo => (
      <TodoItem
        name={todo.name}
        onToggle={sm.will(toggleTodo, todo.id)}
      />
    ))
  }

  render() {
    return <ul>{this.renderTodos()}</ul>
  }
}

const sm = StateManager.from({
  todos: [
    {id: 1, name: 'Buy some groceries'},
    {id: 2, name: 'Buy more groceries'}
  ]
})

ReactDOM.render(
  <Provider stateManager={sm}>
    <TodoList />
  </Provider>,
  document.getElementById('app-root')
)

Batching actions

Managex is very simple and flexible enough to be adapeted to your application requirements. Executing several actions with Managex is just about composing functions.

function add(state, x) {
  return {
    ...state,
    num: state.num + x
  }
}

function mult(state, x) {
  return {
    ...state,
    num: state.num * x
  }
}

function addAndMult(state, x, y) {
  return mult(add(state, x), y)
}

sm.do(addAndMult, 2, 3)

Custom action execution

Managex lets you customize the way actions are executed. The custom action executor can be provided at the time of instancing a new state manager. The default executeAction implementation looks like the following:

function executeAction(stateManager, action, args) {
  return action(stateManager.getState(), ...args)
}

// providing the action executor
const sm = StateManager.from(INITIAL_STATE, executeAction)

Example of providing a custom action executor with crash reporting:

function reportCrash(err, action) {
  console.error('Caught an exception!', err)
  Raven.captureException(err, {
    extra: {
      action: action.toString()
      state: store.getState()
    }
  })
  throw err
}

// custom action executor
function executeAction(stateManager, action, args) {
  try {
    let result = action(stateManager.getState(), ...args)
    // suport promises
    if (result && typeof result.then === 'function') {
      result.catch((err) => reportCrash(err, action))
    }
    return result
  } catch(err) {
    reportCrash(err, action)
  }
}

const sm = StateManager.from(INITIAL_STATE, executeAction)

Alternatively you can make the executeAction asynchonous:

async function executeAction(stateManager, action, args) {
  try {
    return await action(stateManager.getState(), ...args)
  } catch(err) {
    reportCrash(err, action)
  }
}

MIT (c) Yosbel Marín