Creating a typesafe enum using the Symbol operator and typeof

switch.ts

'use strict'

const on = Symbol('on')
const off = Symbol('off')

type switchState = typeof on | typeof off

function changeSwitch(switchState: switchState) {
    switch (switchState) {
      case on:
        return 'Light is on'
      case off: 
        return 'Light is off'  
    }
}

console.log(changeSwitch(off))