代码示例:(标识:js_callback_5)
<!DOCTYPE html>
<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>
运行结果: