Next Js Strict Mode Guide For Optimal Performance

Enabling strict mode in Next Js can significantly improve performance by catching type errors at compile time.

Strict mode helps catch type errors at compile time, preventing runtime errors and improving overall performance.

By default, Next Js uses a hybrid mode that is a mix of strict and loose modes. To enable strict mode, you need to add the 'strictMode' option in the next.config.js file.

Strict mode is enabled by default in Next Js version 12 and later.

Strict Mode in Next.js warns you about potential issues in your application. It's like having a personal quality control manager that checks your code for you.

One of the main warnings you'll see is related to deprecated APIs. These are older ways of doing things that are no longer recommended.

You can enable Strict Mode for a specific part of your application, like a Header or Footer component, without affecting the rest of your app.

React 16.3 introduced a new way to manage refs called createRef, which is a replacement for the legacy string ref API. This new API is more convenient and doesn't have the downsides of the old one.

If you're using legacy context API, you'll see a warning message in Strict Mode. This is because the new context API is more robust and will be the recommended way of doing things in the future.

You can learn more about the new context API and how to migrate to it by reading the documentation.

Strict mode in Next.js helps you detect and fix issues early on, making your development process more efficient. It does this by intentionally double-invoking certain methods, making it easier to spot problems.

This includes class component constructor, render, and shouldComponentUpdate methods, class component static getDerivedStateFromProps method, function component bodies, state updater functions, and functions passed to useState, useMemo, or useReducer. These methods will be double-invoked in development mode only.

In React 18, React DevTools will dim the logs from the second call, and you can also choose to suppress them completely.

Strict mode can also help find bugs in Effects. Every Effect has some setup code and may have some cleanup code. React will run one extra setup+cleanup cycle in development for every Effect, which can help reveal subtle bugs that are hard to catch manually.

Here are some common issues that strict mode can help you detect:

To fix these issues, you can follow these steps:

By following these steps and enabling strict mode in your Next.js app, you can catch issues early on and make your development process more efficient.

You can enable Strict Mode for specific parts of your application, giving you more control over where checks run.

Strict Mode will not run against components like Header and Footer, but it will run on Sidebar and Content, as well as all components inside them.

This means you can choose which parts of your app to prioritize for optimization and error checking.

You're likely to see deprecation warnings in your Next.js app when using Strict Mode. findDOMNode is one of the deprecated APIs that can cause warnings.

To fix deprecation warnings, you can replace findDOMNode with a ref passed to your custom component and then forwarded to the DOM using ref forwarding.

This approach makes it explicit and avoids refactoring hazards. Alternatively, you can add a wrapper DOM node in your component and attach a ref directly to it.

If you're getting warnings about UNSAFE_ class lifecycle methods, you can replace them with alternative methods. Legacy context is another deprecated API that can cause warnings, and you can replace it with the new context API.

Legacy string refs can also cause warnings, and you can replace them with the new ref API.