在一个div中单击关闭到她的div

<div id="mainDiv">
  <div id="childDiv">
    <!-- 子div的内容 -->
  </div>
</div>

#childDiv {
  display: none;
}

document.getElementById("mainDiv").addEventListener("click", function() {
  var childDiv = document.getElementById("childDiv");
  if (childDiv.style.display === "none") {
    childDiv.style.display = "block";
  } else {
    childDiv.style.display = "none";
  }
});