js按钮开关灯效果

body id=“bg”
button class=“btn”>开关灯</button
script>
var btn = document.querySelector(’.btn’);
var i = 0;
var body = document.getElementById(‘bg’)
btn.onclick = function() {
if (i == 1) {
bg.style.backgroundColor = ‘white’;
i++;
} else {
bg.style.backgroundColor = ‘black’;
i = 1;
}
}
</script