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state-actuator

state-actuator is a state management library that expands on the common "reducer" style of state management. It differs from vanilla React useReducer or Redux in the following ways:

  • All state changes are driven by the submission of a message to the state actuator.
  • Asynchronous state changes are built-in allowing the reducer to return Promises of messages.
  • Messages sent to one actuator can be handled by another. When using state-actuator with React components, it allows a child component to send messages to a parent or ancestor.
  • The implementation uses ES2018 AsyncIterator, which allows for customizing the processing of messages and models.

Why state-actuator

There are a lot of choices for state management, both in the React ecosystem and beyond. I wanted to explore a state system that imagines application or component state as an (asynchronous) iteration over instances of models. What drives the changes to the model? Messages. Messages have been used in GUI application development for decades, and messages provide a structured but flexible mechanism to implement UI changes.

ES2018 introduced asynchronous iteration to the JavaScript language. This means we can now model application state using basic language features such as Promises and Iterators.

Getting Started

Install

$ npm install state-actuator

or

$ yarn add state-actuator

Install with React

If you're planning on using state-actuator to manage state for React components, you also need to make sure react and hoist-non-react-statics is installed. (Those packages are not specified as peer dependencies since they're necessary only when importing the React-specific HOC.)

$ npm install react hoist-non-react-statics

or

$ yarn add react hoist-non-react-statics

Usage Example

The state actuator needs two functions to manage your state. The first is an init() function which creates an initial value for the state. The second is an update() function to process messages into new instances of the model.

function init() {
  return { value: "" }
}

function update(model, msg) {
  switch (msg.type) {
    case "AddDigit":
      return { value: model.value + msg.digit }
    case "DeleteDigit:
      return { value: model.value.slice(0, -1) }
  }
}

const actuator = StateActuator({ init, update })

Concepts

Models

The Model is the interface that defines the structure of the state. A model should contain all the properties that change over time.

Messages

Messages are operations that change the state of the component. They typically represent user actions, but they might also represent changes from the outside world. For example, a message ChangeLocation might be sent every time the OS notifies the app that the location has changed. (See "Subscriptions" below.)

Views

Views are responsible for two crucial parts of an application: (1) rendering the UI based on current state and (2) sending messages based on user actions from the UI.

Subscriptions

A subscription is an optional feature in state actuators. It allows messages to be sent from sources other than the UI view.

Context

Context provides access to state that is managed outside state-actuator. For example, if you're populating your model from a database connection, the Context could include a database session object.

Integrations

See how to use state-actuator with React components: react-integration.md