<!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: 200px;
height: 200px;
background: red;
}
</style>
</head>
<body>
<div id="box"></div>
<script>
var box = document.getElementById('box')
var isRed = true
box.onclick = function () {
if (isRed) {
box.style.background = 'green'
} else {
box.style.background = 'red'
}
// 不管走if还是else都取反
isRed = !isRed
}
</script>
</body>
</html>
