Using JavaScript functions to implement user interface interaction

<button onclick="alert('您点击了按钮')">点击我</button>

<script>
    function changeColor() {
        document.getElementById("text").style.color = "red";
    }
</script>

<p id="text" onmouseover="changeColor()">我的颜色将在鼠标移入时变为红色</p>

<form>
    <input type="text" id="age" placeholder="请输入您的年龄">
    <button onclick="checkAge()">提交</button>
</form>

<script>
    function checkAge() {
        var age = document.getElementById("age").value;
        if (isNaN(age)) {
            alert("请输入数字！");
        } else if (age < 18) {
            alert("未满18岁！");
        } else {
            alert("年龄合法！");
        }
    }
</script>

<a href="#contact">联系我们</a>

// 具体实现锚点跳转的代码需要写在页面底部
<a name="contact"></a>

<div class="menu">
    <a href="#" onclick="showContent('home')">首页</a>
    <a href="#" onclick="showContent('about')">关于我们</a>
    <a href="#" onclick="showContent('product')">产品介绍</a>
    <a href="#" onclick="showContent('contact')">联系我们</a>
</div>

<div id="home" class="content">这是首页</div>
<div id="about" class="content">这是关于我们</div>
<div id="product" class="content">这是产品介绍</div>
<div id="contact" class="content">这是联系我们</div>

<script>
    function showContent(id) {
        var contents = document.getElementsByClassName("content");
        for (var i = 0; i < contents.length; i++) {
            contents[i].style.display = "none";
        }
        document.getElementById(id).style.display = "block";
    }
</script>