请问这个轮播图的bug出在了哪里？

var pic = document.getElementsByTagName("img0")[0]; img后多个0

给你改好了

<div id="content">
    <div id="banner">
        <ul class="list">
            <li><img src="img0/01.jpg"></li>
        </ul>
        <ul class="btn">
            <li><a href="#">1</a></li>
            <li><a href="#">2</a></li>
            <li><a href="#">3</a></li>
            <li><a href="#">4</a></li>
            <li><a href="#">5</a></li>
        </ul>
    </div>
</div>
<script type="text/javascript">

var pic = document.getElementsByTagName('img')[0];
var picarr = ['img0/01.jpg', 'img0/02.jpg', 'img0/03.jpg', 'img0/04.jpg', 'img0/05.jpg'];
var timer;
var btnlist = document.querySelectorAll(".btn a");
var index = 0;
timer = setInterval(action, 1000);

function action() {
    index++;
    if (index == 5) {
        index = 0;
    }
    pic.src = picarr[index];
    for (var i = 0; i < 5; i++) {
        btnlist[i].style.background = 'violet';
    }
    btnlist[index].style.background = 'white';
}
for (let j = 0; j < 5; j++) {
    btnlist[j].onmouseover = function() {
        clearInterval(timer);
        for (var k = 0; k < 5; k++) {
            btnlist[k].style.background = 'violet';
        }
        this.style.background = 'white';
        index = j;
        pic.src = picarr[index];
    }
    btnlist[j].onmouseout = function() {
        timer = setInterval(action, 1000);
    }
}

</script>