Simple State Machine

simple-state-machine.js

function createMachine(stateMachineDefinition) {
  const machine = {
    value: stateMachineDefinition.initialState,
    transition(currentState, event) {
      const currentStateDefinition = stateMachineDefinition[currentState]
      const destinationTransition = currentStateDefinition.transitions[event]
      if (!destinationTransition) {
        return
      }
      const destinationState = destinationTransition.target
      const destinationStateDefinition =
        stateMachineDefinition[destinationState]
      destinationTransition.action()
      currentStateDefinition.actions.onExit()
      destinationStateDefinition.actions.onEnter()
      machine.value = destinationState
      return machine.value
    },
  }
  return machine
}
const machine = createMachine({
  initialState: 'off',
  off: {
    actions: {
      onEnter() {
        console.log('off: onEnter')
      },
      onExit() {
        console.log('off: onExit')
      },
    },
    transitions: {
      switch: {
        target: 'on',
        action() {
          console.log('transition action for "switch" in "off" state')
        },
      },
    },
  },
  on: {
    actions: {
      onEnter() {
        console.log('on: onEnter')
      },
      onExit() {
        console.log('on: onExit')
      },
    },
    transitions: {
      switch: {
        target: 'off',
        action() {
          console.log('transition action for "switch" in "on" state')
        },
      },
    },
  },
})
let state = machine.value
console.log(`current state: ${state}`)
state = machine.transition(state, 'switch')
console.log(`current state: ${state}`)
state = machine.transition(state, 'switch')
console.log(`current state: ${state}`)