javastrip中点击销毁计时器再次点击创建计时器，有无人指教下
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>无标题页</title>
<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
</head>
<body>
<button id="app">计时器</button>
<script>
let timer = null
$('#app').click(function () {
console.log('timer', timer)
if (timer) {
clearInterval(timer)
} else {
timer = setInterval(() => {
console.log(1)
}, 1000)
}
})
</script>
</body>
</html>