ea-state-machine

A reactive, modern JavaScript library for general purpose finite state machines with support for navigation and routing.

Overview

This state machine library can be used to track the states and model state transitions of

• business objects,
• application status,
• proccess flows,
• and many more.

Using finite state machine models helps to structure and reason about problems. It supports creating maintainable business rules and source code. Use the state machine diagrams to communicate behaviour and requirements.

Examples:

• Task Management: Once a task is pending, it can be assigned, completed, or canceled. An email is send out to the assinged person.
• Flight status: A plane is IN the gate and then is pushed OUT. Once ON the runway, the plane takes OFF from the origin airport to land ON at the destination.

Usage

Using node/webpack/rollup/browserify:

npm install ea-state-machine

And, if you have not already, install the only peer dependency rxjs.

npm install rxjs

Defining set of possible States.

import { FSM } from 'ea-state-machine'

const state = {
  solid: { name: 'Ice' },
  liquid: { name: 'Water' },
  gas: { name: 'Vapor' }
}

Guards prevent transitions by returning false

const guard = {
  canMelt: (fsm, from, to) => fsm.data.temperature > 0,
  canVaporize: (fsm, from, to) => fsm.data.temperature > 100,
  canCondense: (fsm, from, to) => fsm.data.temperature < 100,
  canFreeze: (fsm, from, to) => fsm.data.temperature >= 0
}

Transition Definitions can be from many to many

const transitionDefiniton = {
    melt: {
      from: state.solid, // can be a single state
      to: [state.liquid], // or multiple targets 
      guards: [guard.canMelt],
      action: () => console.log('melting ...'),
    },
    vaporize: {
      from: () => [state.liquid],
      to: () => [state.gas],
      action: () => console.log('vaporizing ...'),
      guards: [guard.canVaporize],
    },
    condense: {
      from: () => [state.gas],
      to: () => [state.liquid],
      guards: [guard.canCondense],
      action: () => console.log('condenseing ...'),
    },
    freeze: {
      from: () => [state.liquid],
      to: () => [state.solid],
      guards: [guard.canFreeze],
      action: () => console.log('freezing ...'),
    },
  }

Using the above state machine.

// data associated with the fsm
const environment = { 
  temperature: 0 
}

const fsm = new FSM(
  state, // all states
  transitionDefiniton, // transition defitions between states
  state.solid, // optional: start state, if omitted, a transition to the first state needs to happen
  environment // optional: associated data with the state machine
)

fsm.currentState === fsm.states.solid // true

// Can we melt?
fsm.canTranstionTo(fsm.statesliquid) // false
// Heat and update FSM 
fsm.changeData({ environment.temperature = 4})
fsm.canTranstionTo(fsm.states.liquid) // true
fs.transtionTo(fsm.states.liquid)
// // different ways with same effect as above
// fsm.transitionByDefinition(transitionDefiniton.melt)
// fsm.transition(fsm.transitions.filter(t => t.to === fsm.states.liquid))
fsm.currentState.name === 'Water' // true

Documentation

• Design
• States
• Transition Definitions
• Guards
• API

Examples

TODO: One page per example