<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>开关灯</title>
<style>
.open{
background-color: wheat;
}
.close {
background-color: black;
}
button {
width: 100px;
height: 50px;
}
</style>
</head>
<body class = "open close">
<button>开灯</button>
<script>
var btn = document.querySelector('button');
var body = document.querySelector('body');
var flag = 1;
btn.onclick = function() {
if(flag === 1) {