代码示例:(标识:eg_js_use_head)
<!DOCTYPE html>
<html>
<head>
<script>
function myFunction() {
    document.getElementById("demo").innerHTML = "段落已被更改。";
}
</script>
</head>

<body>

<h2>Head 中的 JavaScript</h2>

<p id="demo">一个段落。</p>

<button type="button" onclick="myFunction()">试一试</button>

</body>
</html>
运行结果: