ui.html

<style>
  :root {
    font-family: Inter, sans-serif;
    font-size: 14px;
    color: rgba(0, 0, 0, 0.8);
  }
  body {
    margin: 14px;
  }
  a {
    text-decoration: none;
    color: #18a0fb;
    cursor: pointer;
  }
  p {
    margin: 0;
    line-height: 1.5;
  }
  p.info {
    font-size: 12px;
    opacity: 0.75;
  }
  .layer-name {
    margin-left: 2px;
    padding: 3px 2px 2px;
    border-bottom: 1px dashed #ddd;
    white-space: nowrap;
    text-overflow: ellipsis;
    overflow: hidden;
    line-height: 1.2;
  }
  .primary-button {
    min-width: 100px;
    height: 30px;
    margin: 20px 0;
    display: block;
    cursor: pointer;
    background: #18a0fb;
    border: 1px solid #18a0fb;
    border-radius: 6px;
    padding: 0 16px;
    color: #fff;
    font-size: 11px;
    box-sizing: border-box;
  }
  .primary-button:hover {
    border: 2px solid rgba(0, 0, 0, 0.2);
    padding: 0 15px;
  }
  .layer-order {
    margin: 10px 0;
    padding: 6px 12px 8px;
    border-radius: 2px;
    background: #fafafa;
    display: flex;
    flex-direction: column;
    gap: 6px;
  }
  .layer-order p {
    line-height: 2;
    display: flex;
    align-items: center;
  }
  .layer-order .subtitle {
    opacity: 0.6;
    min-width: 40px;
    font-weight: 500;
  }
  #exchange {
    font-size: 13px;
  }
  #exchange:hover {
    font-weight: 500;
  }
</style>

<p class="info">Choose 2 layers and set the order, then click "Go".</p>
<div class="layer-order">
  <p>
    <span class="subtitle">from</span
    ><span class="layer-name" id="origin-layer"></span>
  </p>
  <p>
    <span class="subtitle">to</span
    ><span class="layer-name" id="target-layer"></span>
  </p>
</div>
<a id="exchange">⇌ Exchange order</a>
<button id="create" class="primary-button">Go</button>
<script>
  let order = false;
  let layerArray, originLayer, targetLayer;

  function showOrder(order) {
    // console.log("order is " + order);
    if (order) {
      document.getElementById("origin-layer").innerHTML = layerArray[1];
      document.getElementById("target-layer").innerHTML = layerArray[0];
    } else {
      document.getElementById("origin-layer").innerHTML = layerArray[0];
      document.getElementById("target-layer").innerHTML = layerArray[1];
    }
  }

  onmessage = (event) => {
    layerArray = event.data.pluginMessage;
    console.log("got this from the plugin code", layerArray);
    showOrder(order);
  };

  document.getElementById("exchange").onclick = () => {
    order = !order;
    // console.log(order);
    showOrder(order);
  };
  document.getElementById("create").onclick = () => {
    parent.postMessage(
      { pluginMessage: { type: "selection-order", order } },
      "*"
    );
  };
</script>