Skip to content

How to solve the `TypeError: Attempted to assign to readonly property` error

New Course Coming Soon:

Get Really Good at Git

I was doing something in my Next.js codebase when I ran into this problem:

TypeError: Attempted to assign to readonly property

Weird! After a bit of debugging I found the problem. I has nothing to do with Next.js, it can happen in any JavaScript codebase.

I had a column in my database where I stored data as JSON.

In my code I was updating this JSON object, using the dot syntax (like data.name = 'Flavio') but I forgot to call JSON.parse() before doing so.

data was not an object, but a string!

Strings are immutable in JavaScript. We can’t update them once defined. Hence the error. The solution was to, obviously, call JSON.parse() before updating the JSON object.

Are you intimidated by Git? Can’t figure out merge vs rebase? Are you afraid of screwing up something any time you have to do something in Git? Do you rely on ChatGPT or random people’s answer on StackOverflow to fix your problems? Your coworkers are tired of explaining Git to you all the time? Git is something we all need to use, but few of us really master it. I created this course to improve your Git (and GitHub) knowledge at a radical level. A course that helps you feel less frustrated with Git. Launching Summer 2024. Join the waiting list!
→ Get my JavaScript Beginner's Handbook
→ Read my JavaScript Tutorials on The Valley of Code
→ Read my TypeScript Tutorial on The Valley of Code

Here is how can I help you: