<!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>Document</title>
<style>
body {
background-color:black ;
}
</style>
</head>
<body>
<button>开灯</button>
<script>
let body=document.querySelector('body');
let button=document.querySelector('button');
let flag=0;
button.addEventListener('click',function(){
if(flag===0){
body.style.backgroundColor='white';
this.innerHTML='关灯';
flag=1;
}
else{
body.style.backgroundColor='black';
this.innerHTML='开灯';
flag=0;
}
})
</script>
</body>
</html>
