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Common Errors in Next.js and How to Fix Them
Next.js is rapidly gaining popularity as a web framework, thanks to its impressive features like static site generation, server-side rendering, and file routing. However, like any other framework, it’s not immune to errors. In this article, we’ll explore some common errors you might encounter while building a Next.js application, along with their solutions.
Hydration Errors
One common error you might encounter in both Next.js and React apps is the hydration error. This error occurs when there’s a mismatch between server- and client-rendered markup and differences in component states. Specifically, Next.js hydration errors arise when you wrap your components or HTML elements with an improper tag.
To fix this error, ensure that you’re not wrapping elements or custom components with improper tags. Instead, use the right “wrapper” elements, such as div, section, or main, to wrap your content. Keep in mind that some third-party components might use the <p> tag as a top-level element, so you’ll need to wrap them inside something semantic to avoid the error.
Document or Window Object Error
When you try to access the window object while the component is still mounting, Next.js will throw an error stating that the document or window is not defined. This error also occurs when you install and use a library that tries to access the window object before the component mounts.
To resolve this error, execute the code that accesses the browser’s window object inside the useEffect() Hook. This ensures that the code only executes after the component has been mounted.
Build Failure Due to Webpack Errors
After running the next build command to build your Next.js application, you might get an error message stating that the build failed due to webpack errors. This error occurs because Next.js v11 and newer use webpack 5 by default, but the error only occurs with webpack 4.
To resolve the issue, enable webpack 5 in your Next.js application by adding the following setting in next.config.js:
API and Slug-Related Errors
A large number of errors in Next.js are related to APIs and slugs. Next.js provides two APIs for data fetching – getStaticPaths and getServerSideProps. However, these functions can throw an error if not properly used.
For example, you might get an error when rendering a page on the server side with the SSG feature, but failing to define the getStaticProps function in the page’s component. The solution is to add a getStaticPaths() function to the page component for /pageName/[slug].
Error When Importing Modules
When importing modules into your Next.js application, you might run into the “Module not found” error. This means that Next.js is unable to locate the module specified in the error message.
To fix this issue, ensure that all Node.js and server-related code is placed inside of the Next.js data-fetching APIs – getServerSideProps, getStaticPaths, or getStaticProps. If that fails to resolve the issue, cross-check that the letter casing of the file you’re attempting to import is correct.
CORS Error – Debugging Next.js API Routes
The /pages/api directory is where you put all the files responsible for handling API requests, with the file name corresponding to the endpoint. Next.js then automatically maps these files to the /api/* URL, which you can access within the application via asynchronous API requests.
To fix the CORS issue, use CORS to handle cross-origin requests. Start by installing cors, then import the library and use it to execute custom middleware just before the API’s response is received.
Catching All Errors in Your Next.js App
When creating your Next.js application, it’s essential to catch all errors and make sure each of them is handled. The best way to do this is at the component level using the try...catch syntax.
By understanding these common errors in Next.js, their causes, and their respective solutions, you can optimize your web app and ensure that it performs as expected.