根据下拉选择设置附加div的颜色

<select id="colorSelect">
  <option value="red">红色</option>
  <option value="blue">蓝色</option>
  <option value="green">绿色</option>
</select>

<div id="colorDiv"></div>

var colorSelect = document.getElementById("colorSelect");
var colorDiv = document.getElementById("colorDiv");

colorSelect.addEventListener("change", function() {
  var selectedColor = colorSelect.value;
  colorDiv.style.backgroundColor = selectedColor;
});