思路：首先获取到这些img这个标签，然后循环出所有的img节点，然后准备几张照片，进行循环，最后在for循环中，放入循环图片的下标
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>随机生成图片</title>
<style>
#div1{
width: 50px;
height: 50px;
margin-left: 20px;
border-radius: 100px;
}
#div1 img{
width: 100%;
border-radius: 100%;
}
</style>
</head>
<body>
<div id="div1" class="d1">
<img src="http://upload.iheima.com/2020/0402/thumb_464_320_1585791787497.png" />
<img src="http://upload.iheima.com/2020/0402/thumb_464_320_1585791944544.png"/>
<img src="http://upload.iheima.com/2020/0402/thumb_464_320_1585791627213.jpg"/>
<img src="http://upload.iheima.com/2020/0401/thumb_464_320_1585735603778.jpg"/>
<img src="http://upload.iheima.com/2020/0401/thumb_464_320_1585735367657.jpg"/>
<img src="http://upload.iheima.com/2020/0401/thumb_464_320_1585734547154.jpg"/>
<img src="http://upload.iheima.com/2020/0401/thumb_484_352_1585734306640.jpeg"/>
</div>
</body>
<script>
var ImgSrc = document.getElementsByTagName('img');
for(var i = 0;i < ImgSrc.length;i++){
var num = Math.ceil(Math.random() * 5);
ImgSrc[i].src="add" + num + ".jpg"
}
</script>
</html>
其中有六张图片在文件夹中
