<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.box{
width: 100px;
height: 100px;
background: blueviolet;
line-height: 70px;
color: #000;
}
</style>
<script>
function scc(n){
var arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "A", "B", "C", "D", "E", "F" ];
var num = "";
for(i = 0 ; i < n; i++){
var position = Math.floor(Math.random() * (arr.length - 1));
num += arr[position];
}
document.getElementsByClassName("box").innerHTML = num;
console.log("num",num,document.getElementsByClassName("box").innerHTML)
}
</script>
</head>
<body>
<div class="box">111111</div>
<button onclick="scc(8)">点击我</button>
</body>
</html>
当设置 <div id="box">111111</div>的时候为什么会生效？但是用<div class="box">111111</div>的时候就不生效？
