仅当选中复选框时才显示文本框，如果未选中，则不将字段保存到数据库中

<input type="checkbox" id="checkbox" onchange="toggleTextbox()">
<input type="text" id="textbox" style="display: none;">

function toggleTextbox() {
  var checkbox = document.getElementById("checkbox");
  var textbox = document.getElementById("textbox");
  
  if (checkbox.checked) {
    textbox.style.display = "block";
  } else {
    textbox.style.display = "none";
  }
}

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

app.use(express.urlencoded({ extended: true }));

app.post("/submit", (req, res) => {
  if (req.body.checkbox === "on") {
    // 保存文本框的值到数据库中
    const textboxValue = req.body.textbox;
    // TODO: 数据库保存逻辑
  }
  
  res.send("Form submitted successfully!");
});

app.listen(3000, () => {
  console.log("Server started on port 3000");
});