A Stop Light state machine class built on Node.js EventEmitter

stoplight.js

import { deepStrictEqual } from 'assert/strict';
import { EventEmitter } from 'events';

class StopLight extends EventEmitter {
	static _data = new Map([
		[ 'GO', { color: 'green' } ],
		[ 'STOP', { color: 'red' } ],
		[ 'SLOW', { color: 'yellow' } ]
	])

	constructor (timers) {
		super()

		this.timers = timers

		this.on('go', function () {
			this.state = 'GO'
			this.log()
		})

		this.on('slow', function () {
			this.state = 'SLOW'
			this.log()
		})

		this.on('stop', function () {
			this.state = 'STOP'
			this.log()
		})

		this.go()
	}

	get data () {
		return StopLight._data.get(this.state)
	}

	go () {
		this.emit('go')
		setTimeout(() => this.slow(), this.timers.GO)
	}

	slow () {
		this.emit('slow')
		setTimeout(() => this.stop(), this.timers.SLOW)
	}

	stop () {
		this.emit('stop')
		setTimeout(() => this.go(), this.timers.STOP)
	}

	log () {
		console.log(`State: ${this.state.padEnd(4)} | Data: ${JSON.stringify(this.data).padEnd(18)} | Timer: ${this.timers[this.state]}`)
	}
}

const stopLight = new StopLight({ GO: 2000, SLOW: 1000, STOP: 3000 })

stopLight.on('go', () => {
	deepStrictEqual(stopLight.state, 'GO')
	deepStrictEqual(stopLight.data, StopLight._data.get('GO'))
})

stopLight.on('slow', () => {
	deepStrictEqual(stopLight.state, 'SLOW')
	deepStrictEqual(stopLight.data, StopLight._data.get('SLOW'))
})

stopLight.on('stop', () => {
	deepStrictEqual(stopLight.state, 'STOP')
	deepStrictEqual(stopLight.data, StopLight._data.get('STOP'))
})