为拖放区域中的selects创建唯一in

<select id="select1">
  <option value="option1">Option 1</option>
  <option value="option2">Option 2</option>
  <option value="option3">Option 3</option>
</select>

<select id="select2">
  <option value="option4">Option 4</option>
  <option value="option5">Option 5</option>
  <option value="option6">Option 6</option>
</select>

var selectedOption;

function dragStart(event) {
  selectedOption = event.target.value;
}

<div id="dropzone" ondrop="drop(event)" ondragover="allowDrop(event)">
  <input type="text" id="uniqueId" readonly>
</div>

function drop(event) {
  event.preventDefault();
  document.getElementById("uniqueId").value = "in" + selectedOption;
}

function allowDrop(event) {
  event.preventDefault();
}