Stop light state machine

statemachine.js

class StateMachine {
  constructor(initialState, transitions) {
    this.state = initialState
    this.transitions = transitions
  }

  transition(next) {
    const nextState = this.transitions[this.state][next]
    if (!nextState) throw new Error(`invalid: ${this.state} -> ${next}`)
    this.state = nextState
  }
}

const machine = new StateMachine('green', {
  green: {
    TIMER: 'orange'
  },
  orange: {
    TIMER: 'red'
  },
  red: {
    TIMER: 'green'
  }
})

setInterval(() => {
  machine.transition('TIMER')
  console.log(machine.state)
}, 1000)