state machine implement referred to https://kentcdodds.com/blog/implementing-a-simple-state-machine-library-in-javascript

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}`);      // current state: off
state = machine.transition(state, 'switch'); // transition action for "switch" in "off" state
console.log(`current state: ${state}`);      // current state on
state = machine.transition(state, 'switch'); // transition action for "switch" in "on" state
console.log(`current state: ${state}`);      // current state off