用原生JavaScript写一个带表单的弹出窗口，点击表单中的确定，弹出框关闭

HTML代码：

<button id="openModal">打开弹出窗口</button>
<div id="modal" class="modal">
  <div class="modal-content">
    <span class="close">&times;</span>
    <h2>弹出窗口</h2>
    <form>
      <label for="name">姓名：</label>
      <input type="text" id="name" name="name"><br><br>
      <label for="age">年龄：</label>
      <input type="number" id="age" name="age"><br><br>
      <button type="submit" id="submit">确定</button>
    </form>
  </div>
</div>

CSS代码：

.modal {
  display: none;
  position: fixed;
  z-index: 1;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  overflow: auto;
  background-color: rgba(0, 0, 0, 0.4);
}

.modal-content {
  background-color: #fefefe;
  margin: 15% auto;
  padding: 20px;
  border: 1px solid #888;
  width: 60%;
}

.close {
  color: #aaa;
  float: right;
  font-size: 28px;
  font-weight: bold;
}

.close:hover,
.close:focus {
  color: black;
  text-decoration: none;
  cursor: pointer;
}

JavaScript代码：

// 获取元素
var openModalBtn = document.getElementById("openModal");
var modal = document.getElementById("modal");
var closeModalBtn = document.getElementsByClassName("close")[0];
var submitBtn = document.getElementById("submit");

// 点击打开弹出窗口按钮
openModalBtn.onclick = function() {
  modal.style.display = "block";
}

// 点击关闭按钮
closeModalBtn.onclick = function() {
  modal.style.display = "none";
}

// 点击确定按钮
submitBtn.onclick = function() {
  // 获取表单中的值
  var name = document.getElementById("name").value;
  var age = document.getElementById("age").value;
  
  // 对表单进行简单校验
  if (name === "" || age === "") {
    alert("姓名和年龄不能为空！");
  } else {
    // 弹出框关闭
    modal.style.display = "none";
  }
}

// 点击弹出框外部区域，弹出框关闭
window.onclick = function(event) {
  if (event.target == modal) {
    modal.style.display = "none";
  }
}

效果如下：