<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div class="box">1</div>
<div class="box">2</div>
<div class="box">3</div>
<script>
    let a =document.getElementsByClassName('box');
    console.log(a);
    // let a =document.getElementsByTagName()
    // 通过class获取
    // 通过标签名获取
    console.log(a.length);
    // 查看有多少个名字叫box的
    console.log(a[0]);
    //获取第一个
    a[1].innerHTML = 'zy'
    // 添加内容




</script>
</body>
</html>