bodyParser.urlencoded(options)

Returns middleware that only parses urlencoded bodies. This parser accepts only UTF-8 encoding of the body and supports automatic inflation of gzip and deflate encodings.

A new body object containing the parsed data is populated on the request object after the middleware (i.e.req.body). This object will contain key-value pairs, where the value can be a string or array (when extended isfalse), or any type (when extended is true).

Options

The urlencoded function takes an option options object that may contain any of the following keys:

extended

The extended option allows to choose between parsing the URL-encoded data with the querystring library (when false) or the qs library (when true). The "extended" syntax allows for rich objects and arrays to be encoded into the URL-encoded format, allowing for a JSON-like experience with URL-encoded. For more information, pleasesee the qs library.

bodyParser.urlencoded 中设置 extended 为 true 和为 false 有什么区别吗？

按照楼上大哥 说的倒是能跑通了，但是后面提交数据的时候需要将 extended: false 改为
extended: true
否则会报错：
TypeError: Cannot read property '_id' of undefined

相关资料：
通常 POST 内容的格式是 application/x-www-form-urlencoded, 因此要用下面的方式来使用：
app.use(require('body-parser').urlencoded({extended: true}))
见：
https://github.com/expressjs/body-parser

首先翻译这句英文，大概的意思就是新版的express中已经不包含bodyparser了，那就需要大家单独安装bodyparser，安装命令是npm install body-parser,然后在app.js中加载body-parser模块var bodyParser = require('body-parser')，把app.use(express.bodyParser())替换成app.use(bodyParser.urlencoded({ extended: false }))，这样调试就没问题了。