Javascript Accordion更改img取决于它是打开还是关闭

<div class="accordion">
  <div class="panel">
    <div class="panel-header" onclick="togglePanel(1)">
      <h2>面板标题1</h2>
      <img id="img1" src="closed.png" alt="关闭图标">
    </div>
    <div id="panel1" class="panel-content">
      <!-- 面板内容1 -->
    </div>
  </div>
  <div class="panel">
    <div class="panel-header" onclick="togglePanel(2)">
      <h2>面板标题2</h2>
      <img id="img2" src="closed.png" alt="关闭图标">
    </div>
    <div id="panel2" class="panel-content">
      <!-- 面板内容2 -->
    </div>
  </div>
</div>

.panel-header {
  cursor: pointer;
}

.panel-content {
  display: none;
}

.panel-content.active {
  display: block;
}

function togglePanel(panelNumber) {
  var panel = document.getElementById("panel" + panelNumber);
  var img = document.getElementById("img" + panelNumber);

  if (panel.style.display === "none") {
    panel.style.display = "block";
    img.src = "opened.png";
  } else {
    panel.style.display = "none";
    img.src = "closed.png";
  }
}