如何根据选定的下拉列表获取自动编号

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

<input type="text" id="autoNumber" readonly>

const dropdown = document.getElementById("dropdown");
const autoNumber = document.getElementById("autoNumber");

dropdown.addEventListener("change", function() {
  const selectedOption = dropdown.value;
  const autoId = generateAutoId(selectedOption);
  autoNumber.value = autoId;
});

function generateAutoId(option) {
  // 根据选项生成自动编号的逻辑
  // 可以使用条件语句或映射表来实现不同选项对应不同编号的逻辑
  // 示例：假设选项1对应编号A，选项2对应编号B，选项3对应编号C
  if (option === "option1") {
    return "A";
  } else if (option === "option2") {
    return "B";
  } else if (option === "option3") {
    return "C";
  }
}

const express = require("express");
const app = express();

app.get("/autoNumber", function(req, res) {
  const selectedOption = req.query.option;
  const autoId = generateAutoId(selectedOption);
  res.send(autoId);
});

function generateAutoId(option) {
  // 根据选项生成自动编号的逻辑
  // 可以使用条件语句或映射表来实现不同选项对应不同编号的逻辑
  // 示例：假设选项1对应编号A，选项2对应编号B，选项3对应编号C
  if (option === "option1") {
    return "A";
  } else if (option === "option2") {
    return "B";
  } else if (option === "option3") {
    return "C";
  }
}

app.listen(3000, function() {
  console.log("Server is running on port 3000");
});