TypeError: Cannot assign to read only property 'userId' of object '#<Object>'

Question

This code worked previously, but now that I upgraded my expo version I am getting the error

TypeError: Cannot assign to read only property 'userId' of object '#'

export interface CurrentUser {
  userId: string;
  ...
}

This is the creation of the object

import { CurrentUser } from "../types/CurrentUser";

let currentUser: CurrentUser|null = null;

This is the assignment that is throwing the error.

export const setUserToken = async (tokenData: TokenResponse) => {
  if (tokenData) {
    currentUser = {
      userId: "",
      ...
    };
  }
  try {
    await currentUserStore.setState(currentUser);
    const result = await setClientsInfoByUsername();
}

export const setClientsInfoByUsername = async () => {
const data = await httpPost(...);

if (currentUser) {
currentUser.userId = data?.employee_id || ""; //Throws error
}

I'm not super familiar with React Native, so any help would be much appreciated.

I'm using expo version 54.0.21

I left out the line before my property assignment, I have a null check in place. — Dftba45
– Dftba45, Commented Nov 3 at 20:43
It is created as an interface and imported in. I will add that code to the question — Dftba45
– Dftba45, Commented Nov 3 at 21:20
thats at typescript/compile time. this error is a runtime error. thats what we need to know — Daniel A. White
– Daniel A. White, Commented Nov 3 at 21:33
When and where is currentUser being assigned. We see that you import the type. But you haven't shown the value. It's the value that is for some reason read-only. It's unclear why but it strongly implies you're not supposed to change it. — VLAZ
– VLAZ, Commented Nov 4 at 5:51

Alparslan ŞEN · Accepted Answer · 2025-11-03 20:39:10Z

-1

The error means you're trying to change a value on an object that’s either null or read-only.In your code, currentUser starts as null, so this line fails:

currentUser.userId = data?.employee_id || "";

You can fix it by giving currentUser an initial value:


let currentUser: CurrentUser = { userId: "" };
currentUser.userId = data?.employee_id || "";

Or, if it can be null:

if (currentUser) {
  currentUser.userId = data?.employee_id || "";
}

answered Nov 3 at 20:39

Alparslan ŞEN

6961 gold badge7 silver badges28 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

VLAZ Nov 4 at 5:49

This is not the error you get when trying to assign a property to null. The error only shows up when it's an object but the property that you're trying to assign is not writeable. jsbin.com/bilezupafa/1/edit?js,console

Collectives™ on Stack Overflow

TypeError: Cannot assign to read only property 'userId' of object '#<Object>'

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related