domHtml += "<div class=\"PopupWindow_end\" onclick=\"changeQdgDetail(this, "+data.ccssbh+")\" >" + " <span>" + "展开详情" +" " +"▼"+ "</span>" + "</div>"+ "<div id='" + data.ccssbh + "' class='pop' name='myPop' style='height: 300px;width: 340px; position: absolute;display: none;background: white;overflow: scroll;z-index: 999;right: -2px;bottom: -300px'></div>"; 如果点击changeQdgDetail（）后下拉弹框并把展开详情改成收回，点击时可收缩弹窗的拼接代码，用if语句编写

您可以尝试使用以下的代码来实现您的需求：

let domHtml = "<div class=\"PopupWindow_end\"  onclick=\"changeQdgDetail(this, "+data.ccssbh+")\" >" +
              " <span>" + (isPopupOpen ? "收回详情" : "展开详情") +" "  + (isPopupOpen ? "▲" : "▼") + "</span>" +
              "</div>" +
              "<div id='" + data.ccssbh + "' class='pop' name='myPop' style='height: 300px;width: 340px; position: absolute;display: " + (isPopupOpen ? "block" : "none") + ";background: white;overflow: scroll;z-index: 999;right: -2px;bottom: -300px'></div>";

// where isPopupOpen is a boolean variable that indicates whether the popup is open or not

function changeQdgDetail(element, id) {
  let popup = document.getElementById(id);
  let span = element.querySelector("span");
  if (popup.style.display === "none") {
    popup.style.display = "block";
    span.textContent = "收回详情 ▲";
    isPopupOpen = true;
  } else {
    popup.style.display = "none";
    span.textContent = "展开详情 ▼";
    isPopupOpen = false;
  }
}

这段代码使用了一个名为 `isPopupOpen` 的布尔变量来跟踪弹出窗口是否已打开。在 `domHtml` 变量中，我们使用三元运算符来根据该变量的状态来设置展开/收回详情的文本和箭头符号。在 `changeQdgDetail` 函数中，我们检查弹出窗口的当前状态，并根据需要更新文本和箭头符号，并将 `isPopupOpen` 变量相应地设置为 `true` 或 `false`。