如何触发modal点击功能

<button id="modalBtn">点击打开modal框</button>

<div id="modal" class="modal">
  <div class="modal-content">
    <span class="close">&times;</span>
    <p>这是一个modal框的内容。</p>
  </div>
</div>

.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: 80%;
}

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

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

// 获取触发modal的按钮元素
var modalBtn = document.getElementById("modalBtn");

// 获取modal框元素
var modal = document.getElementById("modal");

// 获取关闭按钮元素
var closeBtn = document.getElementsByClassName("close")[0];

// 点击按钮时显示modal框
modalBtn.addEventListener("click", function() {
  modal.style.display = "block";
});

// 点击关闭按钮时隐藏modal框
closeBtn.addEventListener("click", function() {
  modal.style.display = "none";
});

// 点击modal框外部区域时隐藏modal框
window.addEventListener("click", function(event) {
  if (event.target == modal) {
    modal.style.display = "none";
  }
});