Express JS中Post方法req.body始终为undefined的问题求助

问题场景 #

配置了app.use(express.json())后，POST请求的req.body仍返回undefined，相关代码、请求示例及错误输出如下：

原代码 #

const express = require("express");
const path = require("path");
const { open } = require("sqlite");
const sqlite3 = require("sqlite3");

const dbPath = path.join(__dirname, "moviesData.db");

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

let database = null;

const initializeDBAndServer = async () => {
  try {
    database = await open({
      filename: dbPath,
      driver: sqlite3.Database,
    })
    app.listen(5353, () => {
      console.log(`server is running at http://localhost:5353/`)
    })
  } catch (error) {
    console.log(`error: ${error.message}`);
    process.exit(1)
  }
}

initializeDBAndServer();

app.post("/myId", async (req, res) => {
  const { id } = req.body;
  console.log(`requested Id is ${id}`);
  res.send(`requested Id id ${id}`);
})

原请求示例 #

POST http://localhost:5353/myId/
Content-Type: "application/json"

{
  "id": 123456 
}

错误输出 #

requested Id is undefined

问题原因 #

1. 请求头格式错误：Content-Type字段带了多余的双引号，正确的Content-Type: application/json不需要加引号，引号会导致Express的JSON解析器无法识别请求体格式，从而无法解析出req.body。
2. 路由定义为/myId，但请求URL是/myId/（末尾多了斜杠），虽然Express默认会处理这种情况，但严格匹配时可能引发不必要的重定向干扰。

修正后的完整代码 #

const express = require("express");
const path = require("path");
const { open } = require("sqlite");
const sqlite3 = require("sqlite3");

const dbPath = path.join(__dirname, "moviesData.db");

const app = express();
// 只保留JSON解析中间件即可，urlencoded用于处理表单数据，此处无需配置
app.use(express.json());

let database = null;

const initializeDBAndServer = async () => {
  try {
    database = await open({
      filename: dbPath,
      driver: sqlite3.Database,
    });
    app.listen(5353, () => {
      console.log(`server is running at http://localhost:5353/`);
    });
  } catch (error) {
    console.log(`error: ${error.message}`);
    process.exit(1);
  }
};

initializeDBAndServer();

app.post("/myId", async (req, res) => {
  const { id } = req.body;
  console.log(`requested Id is ${id}`);
  // 修正响应中的拼写错误（原代码是"id id"）
  res.send(`requested Id is ${id}`);
});

正确的请求格式 #

POST http://localhost:5353/myId
Content-Type: application/json

{
  "id": 123456 
}

验证要点 #

• 确保请求的Content-Type字段没有多余的双引号
• 保持请求URL与路由定义一致（/myId而非/myId/）
• 移除不需要的express.urlencoded()中间件，避免不必要的解析干扰

内容的提问来源于stack exchange，提问作者King Kiran