JS实现警灯效果红蓝闪烁

代码：

<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>警灯效果红蓝闪烁</title>
    <style>
        /* 调整元素的明暗 */
        /* filter: brightness(100%); */
        .context{
            margin-left: 150px;
        }
        .red{
            float: left;
            width: 50px;
            height: 100px;
            background-color: red;
            border: 50px solid red;
            border-top-left-radius: 50px;
            border-top-right-radius: 50px;
            opacity: 0.5;
        }
        .blue{
            float: left;
            width: 50px;
            height: 100px;
            background-color: blue;
            border: 50px solid blue;
            border-top-left-radius: 50px;
            border-top-right-radius: 50px;
            opacity: 0.5;
        }
    </style>
</head>
<body>
    <div class="context">
        <div class="red">

        </div>
        <div class="blue">

        </div>
    </div>
    <script>
        let redlamp = document.getElementsByClassName('red')[0]
        let bluelamp = document.getElementsByClassName('blue')[0]
        let i=0
        setInterval(o=>{
            if(i%2==0){
                redlamp.style.opacity='1'
                bluelamp.style.opacity='0.5'
                i++
            }else{
                redlamp.style.opacity='0.5'
                bluelamp.style.opacity='1'
                i++
            }
        },300)
    </script>
</body>
</html>

效果图：