根据组合框值填充文本框

<select id="combo">
  <option value="option1">选项1</option>
  <option value="option2">选项2</option>
  <option value="option3">选项3</option>
</select>

<input type="text" id="textbox">

document.getElementById("combo").addEventListener("change", function() {
  var comboValue = this.value;
  var textbox = document.getElementById("textbox");

  if (comboValue === "option1") {
    textbox.value = "选项1的内容";
  } else if (comboValue === "option2") {
    textbox.value = "选项2的内容";
  } else if (comboValue === "option3") {
    textbox.value = "选项3的内容";
  }
});