如何寫好JavaScript

需求： 用js實現紅綠燈效果。
三個狀態用紅（stop）、綠（pass）、黃（wait）
要求用JavaScript讓三個狀態輪流切換，每個狀態停留2s

HTML

 <ul id="traffic" class="stop" >
        <li><span></span></li>
        <li><span></span></li>
        <li><span></span></li>
 </ul>

CSS

  li{
            list-style: none;
        }
        ul li span{
            display: inline-block;
            width: 50px;
            height: 50px;
            background-color: gray;
            margin: 5px;
            border-radius: 50%;
        }

        #traffic.stop li:nth-child(1) span{
            background-color: red;
        } 
         #traffic.wait li:nth-child(2) span{
            background-color: yellow;
        }
    
        #traffic.pass li:nth-child(3) span{
            background-color: green;
        }

JavaScript實現
版本1
缺點：依賴外部變量stataList，currentIndex， 封裝性差了點

const traffic = document.getElementById('traffic');
const statusList = ['stop', 'wait', 'pass'];
var curentIndex=0;
setInterval(() => {
    let state = statusList[curentIndex];
    traffic.className = state;
    curentIndex = (curentIndex+1) % statusList.length;
}, 2000);

版本2 數據抽象
缺點：比版本1好點，不過擴展性較差

const traffic = document.getElementById('traffic');
const stateArr = ['stop', 'wait', 'pass'];
function trafficFn(trafficDom, stateList){
    let currentIndex = 0;
    setInterval( ()=>{
        const state = stateList[currentIndex];
        trafficDom.className = state;
        currentIndex = (currentIndex+1) % stateList.length;
    }, 2000 )
}

trafficFn( traffic, stateArr );

版本3 函數式編程， 抽象出poll方法

const traffic = document.getElementById('traffic');
// const statusList = ['stop', 'wait', 'pass'];

function poll(...fnList){
    let stateInex = 0;

    return function(...args){
        let fn = fnList[stateInex++ % fnList.length];
        return fn.apply(this, args);
    }
}

function setState(state){
    traffic.className = state;
}

// 循環執行這三個函數
let trafficStatePoll = poll(
    setState.bind(null, 'wait'),
    setState.bind(null, 'stop'),
    setState.bind(null, 'pass')
)

setInterval(trafficStatePoll, 2000);