<html>
<body>
<h1>JavaScript 回调</h1>
<p>等待 3 秒(3000 毫秒)让此页面发生变化。</p>
<h1 id="demo"></h1>
<script>
setTimeout(myFunction, 3000);
function myFunction() {
document.getElementById("demo").innerHTML = "I love You !!";
}
</script>
</body>
</html>