How to Fix the Property 'slug' does not exist on type 'ParsedUrlQuery | undefined' Error in Next.js

Learn how to solve the TypeScript error when trying to access dynamic routes in Next.js. Follow our step-by-step guide to effectively work with `getServerSideProps` and `ParsedUrlQuery`.
---
This video is based on the question https://stackoverflow.com/q/69742129/ asked by the user 'Rodrigo' ( https://stackoverflow.com/u/832490/ ) and on the answer https://stackoverflow.com/a/75712678/ provided by the user 'Marek Bareła' ( https://stackoverflow.com/u/16696859/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Property 'slug' does not exist on type 'ParsedUrlQuery | undefined'

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Solving the TypeScript Error: Property 'slug' does not exist on type 'ParsedUrlQuery | undefined'

If you're developing a web application using Next.js and TypeScript, you might run into a common error message when trying to fetch dynamic route parameters. This is typically illustrated by the following message:

[[See Video to Reveal this Text or Code Snippet]]

This error occurs due to TypeScript's strict type checking when the framework is unable to infer the shape of your query parameters. In this post, we will break down why this error arises and how to fix it effectively so you can retrieve your slug as a string in your dynamic pages.

Understanding the Problem

When working with Next.js and the getServerSideProps function, we often want access to the URL parameters passed to our page. For example, if you are trying to get the slug from a URL like /post/my-first-post, you would expect to extract my-first-post as a string from the params. However, due to TypeScript's type definitions, params can be undefined, leading to confusion when you try to access properties like slug.

What You Need to Know

ParsedUrlQuery is the type definition used in Next.js to represent URL query parameters.

By default, TypeScript can’t guarantee that context.params will always have the slug property, especially if it’s undefined.

Properly defining the shape of your parameters will help TypeScript understand what you're working with.

The Solution

To resolve this issue, we will create a custom interface that extends ParsedUrlQuery and explicitly defines slug as a string. This ensures TypeScript recognizes that slug will exist and can be safely accessed.

Step-by-Step Instructions

Import ParsedUrlQuery
We'll need to bring in the ParsedUrlQuery type from the querystring module.

[[See Video to Reveal this Text or Code Snippet]]

Define the Params Interface
Create an interface that extends ParsedUrlQuery to include your specific parameters.

[[See Video to Reveal this Text or Code Snippet]]

Modify getServerSideProps
In your getServerSideProps function, use this new interface to type the params appropriately.

[[See Video to Reveal this Text or Code Snippet]]

Complete Example

Here's what the full code would look like integrating the changes mentioned above:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

With these changes in place, you should no longer see the TypeScript error when attempting to access slug. By explicitly defining the shape of your parameters, you enable TypeScript to verify that you're using the correct types, improving your code's safety and robustness.

Now, you can confidently access your dynamic route parameters in a type-safe way while developing your application with Next.js and TypeScript.

If you have any further questions about using Next.js with TypeScript or need guidance on other topics, feel free to reach out!

Видео How to Fix the Property 'slug' does not exist on type 'ParsedUrlQuery | undefined' Error in Next.js канала vlogize