Node.js TypeError: Cannot read property 'author' of undefined

Question

(UPDATED)

Problem: I can't return all my testing data (as the picture shows) No data show up What I expected should be ->

{"data":[{"id": 1,"title": "title A","content": "content A","createTime": 1612708329045,"author": "Alisa"}, {"id": 2,"title": "title B","content": "content B","createTime": 1612708333855,"author": "Alisa"}],"errno":0}

---

Error message from terminal:

PS C:\Users\jiann\Desktop\JS\Nodejs> node www.js
internal/modules/cjs/loader.js:883
  throw err;
  ^

Error: Cannot find module 'C:\Users\jiann\Desktop\JS\Nodejs\www.js'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:880:15)
    at Function.Module._load (internal/modules/cjs/loader.js:725:27)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at internal/main/run_main_module.js:17:47 {
  code: 'MODULE_NOT_FOUND',
  requireStack: []
}

---

I don't know where went wrong:(. Please let me know if more details are needed, appreciate your help!

My code is below:

Code Block 1 Description: If getting data and message successfully, show "errno":0, if not then show "errno":-1

class BaseModel {
        constructor(data, message) {
            if (typeof data === 'string') {
                this.message = data
                data = null
                message = null
            }
            if (data) {
                this.data = message
            }
            if (message) {
                this.message = message
            }
        }
    }
    class SuccessModel extends BaseModel {
        constructor(data, message) {
            super(data, message)
            this.errno = 0
        }
    }
    class ErrorModel extends BaseModel {
        constructor(data, message) {
            super(data, message)
            this.errno = -1
        }
    }
    module.exports = {
        SuccessModel,
        ErrorModel
    }

Code Block 2 Description:

set router for my blog and user. This code block will set data format in JSON, set URL path, parse query, and return 404 if no router is found.

const querystring = require('querystring')
    const handleBlogRouter = require('./blog-1/src/router/blog')
    const handleUserRouter = require('./blog-1/src/router/user')

    const serverHandle = (req, res) => {
        // set JSON
        res.setHeader('Content-type', 'application/json')

        //get path
        const url = req.url
        req.path = url.split('?')[0]

        //parse query
        req.query = querystring.parse(url.split('?')[0])

        //set blog router
        const blogData = handleBlogRouter(req, res)
        if (blogData) {
            res.end(
                JSON.stringify(blogData)
            )
            return
        }

        //set user router
        const userData = handleUserRouter(req, res)
        if (userData) {
            res.end(
                JSON.stringify(userData)
            )
            return
        }
        
        //no router
        res.writeHead(404, {"Content-type": "text/plain"})
        res.write("404 Not Found\n")
        res.end()
    }

    module.exports = serverHandle

Code Block 3 Description: Use GET and POST to require data from path -> '/api/blog/list' '/api/blog/detail' '/api/blog/new' '/api/blog/update' '/api/blog/del'

const { getList, getDetail } = require('../controller/blog')
    const { SuccessModel, ErrorModel } = require('../model/resModel')

    const handleBlogRouter = (req, res) => {
        const method = req.method // GET POST
        

        
        if (method === 'GET' && req.path === '/api/blog/list') {
            const author = req.query.author || ''
            const keyword = req.query.keyword || ''
            const listData = getList(author, keyword)
            return new SuccessModel(listData)
        }

        
        if (method === 'GET' && req.path === '/api/blog/detail') {
            const id = req.query.id
            const data = getDetail(id)
            return new SuccessModel(data)
        }

        
        if (method === 'POST' && req.path === '/api/blog/new') {
            return {
                msg: 'dummy'
            }
        }

        
        if (method === 'POST' && req.path === '/api/blog/update') {
            return {
                msg: 'dummy'
            }
        }

        
        if (method === 'POST' && req.path === '/api/blog/del') {
            return {
                msg: 'dummy'
            }
        }
    }

    module.exports = handleBlogRouter)

Code Block 4 Description: These are my two testing data.

const getList = (author, keyword) => {
        //fake data
        return [
            {
                id: 1, 
                title: 'title A',
                content: 'content A',
                createTime: 1612708329045,
                author: 'Alisa'
            },
            {
                id: 2, 
                title: 'title B',
                content: 'content B',
                createTime: 1612708333855,
                author: 'Amanda'
            }
        ]
    }

    module.exports = {
        getList
    })

Answer 1

This error means you are accessing <?>.author , but <?> is undefined .

For example, if your error is here:

    if (method === 'GET' && req.path === '/api/blog/list') {
        const author = req.query.author || ''
//      ^^^ TypeError: Cannot read property 'author' of undefined
        const keyword = req.query.keyword || ''

This means req.query is undefined . You can use optional chaining if there is a chance something will be present:

let foo = undefined;

foo.bar; // TypeError: Cannot read property 'bar' of undefined
foo?.bar; // => undefined
foo?.bar.baz; // TypeError: Cannot read property 'baz' of undefined
foo?.bar?.baz; // => undefined

Answer 2

the error is because your server hasn't started properly so all those values you are expecting will be not a available. what command did you use to start the server?