javascript - fetch在请求中附加参数，用node搭的服务器获取参数，获取不到

在react写成的app里面，用fetch发请求，用nodeJS搭的服务器接收请求，fetch的请求需要附加请求参数，是写在body里面吗？我这样写了，但是nodeJS那边打印req.body是undefined

fetch请求的代码：

export const newProject = (projectName)=>dispatch=>{
    return fetch(`${ADDRESS}/settings/createModule`,{
        method: "POST",
          mode: "cors",
         headers: {
            "Content-Type": "application/x-www-form-urlencoded"
          },
          body:projectName
    })
    .then(response=>{
        console.log(response)
    })
}

node服务器的代码：req.hasOwnProperty('body')是false，打印Object.keys(req)里面也没有body

var express = require('express');
var app = express();

app.use(require('cors')());
app.post('/settings/createModule',function(req, res){
    console.log(req.body); //undefined
    console.log(req.hasOwnProperty("body")); //false
    res.status(200);
    res.send(projectID);
})
app.listen(9876, function () {
  console.log('Example app listening on port 9876!');
});

用浏览器查看network，参数有发送成功：好绝望啊