TypeError: undefined is not iterable (cannot read property Symbol(Symbol.iterator)) | TypeScript Community | Page 1

inland ocean Jan 23, 2023, 6:03 AM

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I am getting this error in my middleware file auth.ts at line 4 i.e. import getConfig from '../configs/config'.

I am basically exporting a function from my config.ts as below:

config.ts

import dotenv from 'dotenv';
dotenv.config();

export default function () {
  return {
    port: process.env.PORT,
    databaseUrl: process.env.DB_URL,
    jwtAccessSecret: process.env.JWT_ACCESS_SECRET    
  }
}

auth.ts

import { Request, Response, NextFunction } from "express";
import jwt from 'jsonwebtoken';
import users from '../models/users';
import getConfig from '../configs/config'; // Getting error here
import '../types/express/extendRequest';

const { jwtAccessSecret } = getConfig();
.
.
.

I have used the same import statement in my server.ts, db.ts etc. and it runs without any issue.

Can anyone please help me figure out what the issue is?

Please let me know if any more info is required.

Thank you

harsh halo Jan 23, 2023, 6:06 AM

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you're trying to iterate over undefined, basically

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do you have a stacktrace

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a stacktrace would help a lot

inland ocean Jan 23, 2023, 6:23 AM

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import getConfig from '../configs/config';
           ^
TypeError: undefined is not iterable (cannot read property Symbol(Symbol.iterator))
    at /home/ayush/Ayush Jain/MERN/Monolithic/authServer/src/middlewares/auth.ts:35:59
    at Generator.next (<anonymous>)
    at /home/ayush/Ayush Jain/MERN/Monolithic/authServer/src/middlewares/auth.ts:8:71
    at new Promise (<anonymous>)
    at __awaiter (/home/ayush/Ayush Jain/MERN/Monolithic/authServer/src/middlewares/auth.ts:4:12)
    at authenticateToken (/home/ayush/Ayush Jain/MERN/Monolithic/authServer/src/middlewares/auth.ts:34:85)
    at Layer.handle [as handle_request] (/home/ayush/Ayush Jain/MERN/Monolithic/authServer/node_modules/express/lib/router/layer.js:95:5)
    at trim_prefix (/home/ayush/Ayush Jain/MERN/Monolithic/authServer/node_modules/express/lib/router/index.js:328:13)
    at /home/ayush/Ayush Jain/MERN/Monolithic/authServer/node_modules/express/lib/router/index.js:286:9
    at Function.process_params (/home/ayush/Ayush Jain/MERN/Monolithic/authServer/node_modules/express/lib/router/index.js:346:12)

harsh halo Jan 23, 2023, 6:27 AM

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what's auth.ts:35

inland ocean Jan 23, 2023, 6:28 AM

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harsh halo what's `auth.ts:35`

const [bearer, accessTokenHeader, refreshTokenHeader] = req.headers['authorization'] && req.headers['authorization'].split(' ') as any;```

harsh halo Jan 23, 2023, 6:28 AM

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so req.headers['authorization'] is undefined

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you shouldn't be trying to destructure from a possibly nonexistant value, ts wouldve told you that but you used as any lol

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isn't it usually Authorization?

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also you can use ?. there rather than doing the a && a.b thing
then provide a default/defaults

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https://mdn.io/Optional_chaining
https://mdn.io/Nullish_coalescing

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or you may want to just check for the auth header being there and just branch from that with just an if

inland ocean Jan 23, 2023, 6:32 AM

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I am actually fairly new to ts. This is my first project using ts so I am the learning phase. But thanks for the explanation and the links.

harsh halo Jan 23, 2023, 6:32 AM

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tip: don't use any or as/<> or ! unless absolutely necessary

inland ocean Jan 23, 2023, 6:33 AM

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Yes I read that somewhere but ts wasnt allowing me destructure the array

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so as a last resort I used any

harsh halo Jan 23, 2023, 6:33 AM

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inland ocean Yes I read that somewhere but ts wasnt allowing me destructure the array

yeah because you don't have an array

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so you disabled ts and now you got a harder-to-trace runtime error

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don't disregard what ts is saying ¯_(ツ)_/¯

inland ocean Jan 23, 2023, 6:35 AM

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harsh halo yeah because you don't have an array

But we know that split method returns an array so isnt ts able to figure that out?

harsh halo Jan 23, 2023, 6:35 AM

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ts is

inland ocean Jan 23, 2023, 6:35 AM

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harsh halo don't disregard what ts is saying ¯\_(ツ)_/¯

Yup learnt my lesson lol

harsh halo Jan 23, 2023, 6:37 AM

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!ts

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bro this doesn't have strictNullChecks on 💀

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sec

inland ocean Jan 23, 2023, 6:39 AM

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Well seems like I got a lot of reading to do 😅

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Also, one last thing

harsh halo Jan 23, 2023, 6:39 AM

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ok seems like this works

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maybe im just misremembering how to write those examples painpeko

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!ts

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goddammit

inland ocean Jan 23, 2023, 6:40 AM

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WTH 😂

harsh halo Jan 23, 2023, 6:40 AM

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needed a typecast haachama_aaaaaaaaaa

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!ts

fathom crystalBOT Jan 23, 2023, 6:40 AM

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const a = ("" as string).split("");
//    ^? - const a: string[]
// guaranteed string

let b: string | undefined = undefined as string | undefined;
//  ^? - let b: string | undefined
// your case, you don't know if the auth header is actually present
const bResult1 = b.split("");
//               ^
// 'b' is possibly 'undefined'.
//    ^? - const bResult1: string[]
const bResult2 = b && b.split("");
//    ^? - const bResult2: "" | string[] | undefined```

harsh halo Jan 23, 2023, 6:40 AM

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there, there we go

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finally

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ignore the clutter on b, basically b is what you have

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bResult2 is what you're doing

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split does give an array, yes

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but split is never reached if b is falsy

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because the logical and will short-circuit, giving you that falsy value

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and for any falsy value that isn't a string, there's no iterator, including undefined

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so that's where your error is

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https://mdn.io/logical_and
https://mdn.io/falsy

inland ocean Jan 23, 2023, 6:42 AM

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Ahh it makes so much sense now.

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Sir you are a great teacher I must say 🫡

harsh halo Jan 23, 2023, 6:43 AM

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i am in extreme pain

inland ocean Jan 23, 2023, 6:44 AM

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May I ask why?

harsh halo Jan 23, 2023, 6:44 AM

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[gestures broadly at everything]

inland ocean Jan 23, 2023, 6:47 AM

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Can I add you as a friend if thats okay with you?

inland ocean Jan 23, 2023, 6:47 AM

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harsh halo [gestures broadly at everything]

You depressed or something?

harsh halo Jan 23, 2023, 6:49 AM

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nah just got a lot going on rn, i really shouldn't be here lol

inland ocean Jan 23, 2023, 6:49 AM

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Thanks for your help and prompt response btw, it really saved me a lot of time man. Really appreciate it.

harsh halo Jan 23, 2023, 6:50 AM

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harsh halo https://mdn.io/Optional_chaining https://mdn.io/Nullish_coalescing

anyways from this, did you manage to solve your issue

inland ocean Jan 23, 2023, 6:51 AM

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I am doing that, just let me get a hang of it and I will get back to you if I am stuck.

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btw i sent you friend req

#TypeError: undefined is not iterable (cannot read property Symbol(Symbol.iterator))