原生js轮播图 淡入淡出

<style>
    * {
        padding: 0;
        margin: 0;
        box-sizing: border-box;
    }

    #box {
        width: 300px;
        height: 150px;
        position: relative;
        margin: 0 auto;
        overflow: hidden;
    }

    #box:hover {
        cursor: pointer;
    }

    .pic, #left, #right {
        position: absolute;
    }

    .pic {
        display: none;
        height: 150px;
    }

    #left, #right {
        height: 60px;
        background: #cccccc;
        opacity: 0.6;
        line-height: 60px;
        width: 40px;
        text-align: center;
        top: 0;
        left: 0;
        bottom: 0;
        right: 0;
        display: none;
        transition: all 500ms;
    }

    #right {
        margin: auto 0 auto auto;
    }

    #left {
        margin: auto auto auto 0;
    }

    #box:hover #right, #box:hover #left {
        display: block;
        cursor: pointer;
    }

    #right:hover, #left:hover {
        background-color: white;
        color: red;
        opacity: 1;
    }

</style>
<script>
    //图片数组，左点击按钮，右点击按钮，数组下标
    let pic, left, right, index = 0;
    window.onload = function () {
        pic = document.getElementsByClassName("pic");
        left = document.getElementById("left");
        right = document.getElementById("right");
        //首次要第一张图显示
        pic[0].style.display = "block";

        //左点击效果
        left.onclick = () => {
            pic[index].style.zIndex = "1";
            let temp = index;
            index--;
            if (index === -1) {
                index = pic.length - 1;
            }
            pic[index].style.display = "block";
            let opy = 1, len = 0, w = 300;
            let num = setInterval(() => {
                opy -= 0.01;
                len--;
                pic[temp].style.opacity = opy;
                pic[temp].style.transform = "translateX(" + len + "px) ";
                if (opy <= 0) {
                    clearInterval(num);
                    pic[temp].style.zIndex = "0";
                    pic[temp].style.opacity = 1;
                    pic[temp].style.display = "none";
                    pic[temp].style.transform = "translate(0,0)";
                }
            }, 1);
        };

        //右点击效果
        right.onclick = () => {
            pic[index].style.zIndex = "1";
            let temp = index;
            index++;
            if (index === pic.length) {
                index = 0;
            }
            pic[index].style.display = "block";
            let opy = 1, len = 0;
            let num = setInterval(() => {
                opy -= 0.01;
                len++;
                pic[temp].style.opacity = opy;
                pic[temp].style.transform = "translateX(" + len + "px) ";
                if (opy <= 0) {
                    clearInterval(num);
                    pic[temp].style.zIndex = "0";
                    pic[temp].style.opacity = 1;
                    pic[temp].style.display = "none";
                    pic[temp].style.transform = "translate(0,0)";
                }
            }, 1);
        };
    };
</script>
          
<div id="left">left</div>
<div id="right">right</div>